Elementary Algebra Textbook Solutions Manual Second Edition Department of Mathematics College of the Redwoods 2012-2013 ii Copyright c 2011 in the All parts of this prealgebra textbook are copyrighted name of the Department of Mathematics, College of the Redwoods. They are not in the public domain. However, they are being made available free for use in educational institutions. This oﬀer does not extend to any application that is made for proﬁt. Users who have such applications in mind should contact David Arnold at [email protected] or Bruce Wagner at [email protected] This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ or send a letter to Creative Commons, 171 Second Street, Suite 300, San Francisco, California, 94105, USA. Second Edition: 2012-2013 Contents 1 The 1.1 1.2 1.3 1.4 1.5 Arithmetic of Numbers An Introduction to the Integers Order of Operations . . . . . . The Rational Numbers . . . . . Decimal Notation . . . . . . . . Algebraic Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 7 18 33 47 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Solving Linear Equations 2.1 Solving Equations: One Step . . . . 2.2 Solving Equations: Multiple Steps . 2.3 Solving Equations: Clearing Frations 2.4 Formulae . . . . . . . . . . . . . . . 2.5 Applications . . . . . . . . . . . . . . 2.6 Inequalities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . and Decimals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 . 53 . 60 . 73 . 81 . 91 . 108 3 Introduction to Graphing 3.1 Graphing Equations by Hand . 3.2 The Graphing Calculator . . . 3.3 Rates and Slope . . . . . . . . 3.4 Slope-Intercept Form of a Line 3.5 Point-Slope Form of a Line . . 3.6 Standard Form of a Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 127 140 149 157 168 183 4 Systems 4.1 Solving Systems by Graphing . . 4.2 Solving Systems by Substitution 4.3 Solving Systems by Elimination . 4.4 Applications of Linear Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 205 226 243 259 5 Polynomials 269 5.1 Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 iii CONTENTS iv 5.2 5.3 5.4 5.5 5.6 5.7 Polynomials . . . . . . . . . . . . . . Applications of Polynomials . . . . . Adding and Subtracting Polynomials Laws of Exponents . . . . . . . . . . Multiplying Polynomials . . . . . . . Special Products . . . . . . . . . . . 6 Factoring 6.1 The Greatest Common Factor 6.2 Solving Nonlinear Equations . 6.3 Factoring Trinomials I . . . . 6.4 Factoring Trinomials II . . . . 6.5 Special Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 290 298 303 309 317 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335 335 347 362 378 397 7 Rational Functions 7.1 Negative Exponents . . . . . . . 7.2 Scientiﬁc Notation . . . . . . . . 7.3 Simplifying Rational Expressions 7.4 Solving Rational Equations . . . 7.5 Direct and Inverse Variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413 413 425 433 441 456 8 Quadratic Functions 8.1 Introduction to Radical Notation 8.2 Simplifying Radical Expressions . 8.3 Completing the Square . . . . . . 8.4 The Quadratic Formula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465 465 471 479 494 Second Edition: 2012-2013 . . . . . Chapter 1 The Arithmetic of Numbers 1.1 An Introduction to the Integers 1. The number 5 is 5 units from the origin. 5 units −10 0 5 10 Hence, |5| = 5. 3. The number −2 is 2 units from the origin. 2 units −10 −2 0 10 Hence, | − 2| = 2. 5. The number 2 is 2 units from the origin. 2 units −10 0 Hence, |2| = 2. 1 2 10 CHAPTER 1. THE ARITHMETIC OF NUMBERS 2 7. The number −4 is 4 units from the origin. 4 units −10 −4 0 10 Hence, | − 4| = 4. 9. We have like signs. The magnitudes (absolute values) of −91 and −147 are 91 and 147, respectively. If we add the magnitudes, we get 238. If we preﬁx the common negative sign, we get −238. That is: −91 + (−147) = −238 11. We have like signs. The magnitudes (absolute values) of 96 and 145 are 96 and 145, respectively. If we add the magnitudes, we get 241. If we preﬁx the common positive sign, we get 241. That is: 96 + 145 = 241 13. To add a negative and a positive integer, subtract the smaller magnitude from the larger magnitude (76 − 46 = 30), then preﬁx the sign of the integer with the larger magnitude. Thus, −76 + 46 = −30. 15. We have like signs. The magnitudes (absolute values) of −59 and −12 are 59 and 12, respectively. If we add the magnitudes, we get 71. If we preﬁx the common negative sign, we get −71. That is: −59 + (−12) = −71 17. To add a positive and a negative integer, subtract the smaller magnitude from the larger magnitude (86 − 37 = 49), then preﬁx the sign of the integer with the larger magnitude. Thus, 37 + (−86) = −49. Second Edition: 2012-2013 1.1. AN INTRODUCTION TO THE INTEGERS 3 19. To add a positive and a negative integer, subtract the smaller magnitude from the larger magnitude (85 − 66 = 19), then preﬁx the sign of the integer with the larger magnitude. Thus, 66 + (−85) = −19. 21. We have like signs. The magnitudes (absolute values) of 57 and 20 are 57 and 20, respectively. If we add the magnitudes, we get 77. If we preﬁx the common positive sign, we get 77. That is: 57 + 20 = 77 23. To add a negative and a positive integer, subtract the smaller magnitude from the larger magnitude (127 − 48 = 79), then preﬁx the sign of the integer with the larger magnitude. Thus, −48 + 127 = 79. 25. Subtraction means “add the opposite,” so change the diﬀerence into a sum. −20 − (−10) = −20 + 10 = −10 Subtracting −10 is the same as adding 10. Subtract the magnitudes, and preﬁx with sign of larger number. 27. Subtraction means “add the opposite,” so change the diﬀerence into a sum. −62 − 7 = −62 + (−7) = −69 Subtracting 7 is the same as adding −7. Add the magnitudes, and preﬁx the common negative sign. 29. Subtraction means “add the opposite,” so change the diﬀerence into a sum. −77 − 26 = −77 + (−26) = −103 Subtracting 26 is the same as adding −26. Add the magnitudes, and preﬁx the common negative sign. Second Edition: 2012-2013 CHAPTER 1. THE ARITHMETIC OF NUMBERS 4 31. Subtraction means “add the opposite,” so change the diﬀerence into a sum. −7 − (−16) = −7 + 16 =9 Subtracting −16 is the same as adding 16. Subtract the magnitudes, and preﬁx with sign of larger number. 33. In the expression (−8)6 , the exponent 6 tells us to write the base −8 six times as a factor. Thus, (−8)6 = (−8)(−8)(−8)(−8)(−8)(−8). Now, the product of an even number of negative factors is positive. (−8)6 = 262144 35. In the expression (−7)5 , the exponent 5 tells us to write the base −7 ﬁve times as a factor. Thus, (−7)5 = (−7)(−7)(−7)(−7)(−7). Now, the product of an odd number of negative factors is negative. (−7)5 = −16807 37. In the expression (−9)2 , the exponent 2 tells us to write the base −9 two times as a factor. Thus, (−9)2 = (−9)(−9). Now, the product of an even number of negative factors is positive. (−9)2 = 81 39. In the expression (−4)4 , the exponent 4 tells us to write the base −4 four times as a factor. Thus, (−4)4 = (−4)(−4)(−4)(−4). Now, the product of an even number of negative factors is positive. (−4)4 = 256 Second Edition: 2012-2013 1.1. AN INTRODUCTION TO THE INTEGERS 5 41. To calculate the expression −562 − 1728, enter the expression -562-1728 using the following keystrokes. (-) 5 6 − 2 1 7 2 8 ENTER The result is shown in the following ﬁgure. Hence, −562 − 1728 = −2290. 43. To calculate the expression −400−(−8225), enter the expression -400-(-8225) using the following keystrokes. (-) 4 0 0 − ( (-) 8 2 2 5 ) ENTER The result is shown in the following ﬁgure. Hence, −400 − (−8225) = 7825. 45. To calculate the expression (−856)(232), enter the expression -856*232 using the following keystrokes. (-) 8 5 6 × 2 3 2 ENTER The result is shown in the following ﬁgure. Hence, (−856)(232) = −198592. Second Edition: 2012-2013 CHAPTER 1. THE ARITHMETIC OF NUMBERS 6 47. To calculate the expression (−815)(−3579), enter the expression -815*-3579 using the following keystrokes. (-) 8 1 × 5 (-) 3 5 7 9 ENTER The result is shown in the following ﬁgure. Hence, (−815)(−3579) = 2916885. 49. To calculate the expression (−18)3 , enter the expression (-18)∧3 using the following keystrokes. ( (-) 1 8 ) ∧ 3 ENTER The result is shown in the following ﬁgure. Hence, (−18)3 = −5832. 51. To calculate the expression (−13)5 , enter the expression (-13)∧5 using the following keystrokes. ( (-) 1 3 ) The result is shown in the following ﬁgure. Hence, (−13)5 = −371293. Second Edition: 2012-2013 ∧ 5 ENTER 1.2. ORDER OF OPERATIONS 1.2 7 Order of Operations 1. The Rules Guiding Order of Operations require that multiplication is applied ﬁrst, then addition. −12 + 6(−4) = −12 + (−24) = −36 Multiply ﬁrst: 6(−4) = −24. Add: −12 + (−24) = −36. 3. In the expression −(−2)5 , the exponent 5 tells us to write the base −2 ﬁve times as a factor. Thus, −(−2)5 = −(−2)(−2)(−2)(−2)(−2) Multiply: (−2)(−2)(−2)(−2)(−2) = −32. −(−2)5 = −(−32) Finally, take the opposite. −(−2)5 = 32 5. First take the absolute value, then negate (take the opposite) of the result. −| − 40| = −(40) = −40 Absolute value: | − 40| = 40 Negate. 7. The Rules Guiding Order of Operations require that division and multiplication must be done in the order that they appear, working from left to right. −24/(−6)(−1) = 4(−1) = −4 Divide: −24/(−6) = 4. Multiply: 4(−1) = −4. 9. The opposite of −50 is 50, or if you wish, the negative of −50 is 50. That is, −(−50) = 50. 11. In the expression −35 , the exponent 5 tells us to write the base 3 ﬁve times as a factor. Thus, −35 = −(3)(3)(3)(3)(3). Note that order of operations forces us to apply the exponent before applying the minus sign. −35 = −243 Second Edition: 2012-2013 8 CHAPTER 1. THE ARITHMETIC OF NUMBERS 13. The Rules Guiding Order of Operations require division and multiplication must be done in the order that they appear, working from left to right. 48 ÷ 4(6) = 12(6) = 72 Divide: 48 ÷ 4 = 12. Multiply: 12(6) = 72. 15. −52 − 8(−8) = −52 − (−64) = −52 + 64 = 12 Multiply ﬁrst: 8(−8) = −64. Add the opposite. Add: −52 + 64 = 12. 17. In the expression (−2)4 , the exponent 4 tells us to write the base −2 four times as a factor. Thus, (−2)4 = (−2)(−2)(−2)(−2). Multiply. An even number of negative signs yield a positive result. (−2)4 = 16 19. The Rules Guiding Order of Operations require that we address exponents ﬁrst, then multiplications, then subtractions. 9 − 3(2)2 = 9 − 3(4) Exponent ﬁrst: (2)2 = 4. = 9 − 12 Multiply: 3(4) = 12. = 9 + (−12) = −3 Add the opposite. Add: 9 + (−12) = −3. 21. We must ﬁrst evaluate the expression inside the absolute value bars. Subtraction means “add the opposite.” 17 − 10|13 − 14| = 17 − 10|13 + (−14)| = 17 − 10| − 1| Add the opposite. Add: 13 + (−14) = −1 = 17 − 10(1) = 17 − 10 Absolute value: | − 1| = 1 Multiply: 10(1) = 10 = 17 + (−10) =7 Add the opposite. Add: 17 + (−10) = 7 Second Edition: 2012-2013 1.2. ORDER OF OPERATIONS 9 23. The Rules Guiding Order of Operations require that we address exponents ﬁrst, then multiplications, then subtractions. −4 + 5(−4)3 = −4 + 5(−64) = −4 + (−320) Exponent ﬁrst: (−4)3 = −64. Multiply: 5(−64) = −320. = −324 Add: −4 + (−320) = −324. 25. The Rules Guiding Order of Operations require evaluate the expression inside the parentheses ﬁrst, then multiply, then subtract. 8 + 5(−1 − 6) = 8 + 5(−1 + (−6)) = 8 + 5(−7) Add the opposite. Add:−1 + (−6) = −7. Multiply: 5(−7) = −35. Add: 8 + (−35) = −27. = 8 + (−35) = −27 27. Following the Rules Guiding Order of Operations, we must ﬁrst simplify the expressions inside the parentheses. Then we can apply the exponents and after that, subtract. (10 − 8)2 − (7 − 5)2 = 22 − 23 Subtract: 10 − 8 = 2; 7 − 5 = 2. =4−8 Square: 22 = 4. Cube: 23 = 8. = 4 + (−8) = −4 Add the opposite. Add: 4 + (−8) = −4. 29. The Rules Guiding Order of Operations require evaluate the expression inside the innermost parentheses ﬁrst. 6 − 9(6 − 4(9 − 7)) = 6 − 9(6 − 4(9 + (−7))); Add the opposite. = 6 − 9(6 − 4(2)); = 6 − 9(6 − 8); Add: 9 + (−7) = 2. Multiply: 4(2) = 8. = 6 − 9(6 + (−8)); = 6 − 9(−2); Add the opposite. Add: 6 + (−8) = −2. = 6 − (−18); = 6 + 18; Multiply: 9(−2) = −18. Add the opposite. = 24 Add: 6 + 18 = 24. Second Edition: 2012-2013 10 CHAPTER 1. THE ARITHMETIC OF NUMBERS 31. The Rules Guiding Order of Operations require evaluate the expression inside the parentheses ﬁrst, then multiply, then subtract. −6 − 5(4 − 6) = −6 − 5(4 + (−6)) Add the opposite. = −6 − 5(−2) = −6 − (−10) Add:4 + (−6) = −2. Multiply: 5(−2) = −10. = −6 + 10 =4 Add the opposite. Add: −6 + 10 = 4. 33. Following the Rules Guiding Order of Operations, simplify the expression inside the parentheses ﬁrst, then apply the exponent, then add and subtract, moving left to right. 9 + (9 − 6)3 − 5 = 9 + 33 − 5 Subtract: 9 − 6 = 3. = 9 + 27 − 5 = 9 + 27 + (−5) Exponent: 33 = 27. Add the opposite. = 36 + (−5) = 31 Add: 9 + 27 = 36. Add: 36 + (−5) = 31. 35. The Rules Guiding Order of Operations require that we address exponents ﬁrst, then multiplications, then subtractions. −5 + 3(4)2 = −5 + 3(16) Exponent ﬁrst: (4)2 = 16. = −5 + 48 Multiply: 3(16) = 48. = 43 Add: −5 + 48 = 43. 37. Following the Rules Guiding Order of Operations, simplify the expression inside the parentheses ﬁrst, then apply the exponent, then add and subtract, moving left to right. 8 − (5 − 2)3 + 6 = 8 − 33 + 6 Subtract: 5 − 2 = 3. = 8 − 27 + 6 Exponent: 33 = 27. = 8 + (−27) + 6 = −19 + 6 Add the opposite. Add: 8 + (−27) = −19. = −13 Add: −19 + 6 = −13. Second Edition: 2012-2013 1.2. ORDER OF OPERATIONS 11 39. We must ﬁrst evaluate the expression inside the absolute value bars. Start with “subtraction means add the opposite.” |6 − 15| − | − 17 − 11| = |6 + (−15)| − | − 17 + (−11)| = | − 9| − | − 28| = 9 − 28 = 9 + (−28) = −19 Add the opposites. Add: 6 + (−15) = −9 and −17 + (−11) = −28 Absolute value: | − 9| = 9 and | − 28| = 28 Add the opposite. Add: 9 + (−28) = −19 41. The Rules Guiding Order of Operations require evaluate the expression inside the innermost parentheses ﬁrst. 5 − 5(5 − 6(6 − 4)) = 5 − 5(5 − 6(6 + (−4))); Add the opposite. = 5 − 5(5 − 6(2)); = 5 − 5(5 − 12); Add: 6 + (−4) = 2. Multiply: 6(2) = 12. = 5 − 5(5 + (−12)); = 5 − 5(−7); Add the opposite. Add: 5 + (−12) = −7. = 5 − (−35); = 5 + 35; Multiply: 5(−7) = −35. Add the opposite. = 40 Add: 5 + 35 = 40. 43. First replace all occurrences of the variables in the expression with open parentheses: 4x2 + 3xy + 4y 2 = 4( )2 + 3( )( ) + 4( )2 Then replace each variable with its given value, and evaluate the expression: 4x2 + 3xy + 4y 2 = 4(−3)2 + 3(−3)(0) + 4(0)2 = 4(9) + 3(−3)(0) + 4(0) = 36 = 36 Substitute −3 for x and 0 for y. Evaluate exponents ﬁrst. Perform multiplications, left to right. Perform additions and subtractions, left to right. 45. First replace all occurrences of the variables in the expression with open parentheses: −8x + 9 = −8( ) + 9 Second Edition: 2012-2013 CHAPTER 1. THE ARITHMETIC OF NUMBERS 12 Then replace each variable with its given value, and evaluate the expression: −8x + 9 = −8(−9) + 9 = 72 + 9 = 81 Substitute −9 for x. Multiply ﬁrst: −8(−9) = 72 Add. 47. First replace all occurrences of the variables in the expression with open parentheses: −5x2 + 2xy − 4y 2 = −5( )2 + 2( )( ) − 4( )2 Then replace each variable with its given value, and evaluate the expression: −5x2 + 2xy − 4y 2 = −5(5)2 + 2(5)(0) − 4(0)2 = −5(25) + 2(5)(0) − 4(0) = −125 = −125 Substitute 5 for x and 0 for y. Evaluate exponents ﬁrst. Perform multiplications, left to right. Perform additions and subtractions, left to right. 49. First replace all occurrences of the variables in the expression with open parentheses: 3x2 + 3x − 4 = 3( )2 + 3( ) − 4 Then replace each variable with its given value, and evaluate the expression: 3x2 + 3x − 4 = 3(5)2 + 3(5) − 4 Substitute 5 for x. = 3(25) + 3(5) − 4 = 75 + 15 − 4 Evaluate exponents ﬁrst. Perform multiplications, left to right. = 86 Perform additions and subtractions, left to right. 51. First replace all occurrences of the variables in the expression with open parentheses: −2x2 + 2y 2 = −2( )2 + 2( )2 Then replace each variable with its given value, and evaluate the expression: −2x2 + 2y 2 = −2(1)2 + 2(−2)2 Substitute 1 for x and −2 for y. = −2(1) + 2(4) = −2 + 8 Evaluate exponents ﬁrst. Perform multiplications, left to right. =6 Perform additions and subtractions, left to right. Second Edition: 2012-2013 1.2. ORDER OF OPERATIONS 13 53. First replace all occurrences of the variables in the expression with open parentheses: −3x2 − 6x + 3 = −3( )2 − 6( ) + 3 Then replace each variable with its given value, and evaluate the expression: −3x2 − 6x + 3 = −3(2)2 − 6(2) + 3 = −3(4) − 6(2) + 3 = −12 − 12 + 3 = −21 Substitute 2 for x. Evaluate exponents ﬁrst. Perform multiplications, left to right. Perform additions and subtractions, left to right. 55. First replace all occurrences of the variables in the expression with open parentheses: −6x − 1 = −6( ) − 1 Then replace each variable with its given value, and evaluate the expression: −6x − 1 = −6(1) − 1 = −6 − 1 = −7 Substitute 1 for x. Multiply ﬁrst: −6(1) = −6 Subtract. 57. First replace all occurrences of the variables in the expression with open parentheses: 3x2 − 2y 2 = 3( )2 − 2( )2 Then replace each variable with its given value, and evaluate the expression: 3x2 − 2y 2 = 3(−3)2 − 2(−2)2 Substitute −3 for x and −2 for y. = 3(9) − 2(4) = 27 − 8 Evaluate exponents ﬁrst. Perform multiplications, left to right. = 19 Perform additions and subtractions, left to right. 59. Replace each occurrence of the variables a and b with open parentheses, then substitute 27 for a and −30 for b. 2 2 a2 + b 2 ( ) +( ) = a+b ( )+( ) 2 = Replace variables with open parentheses. 2 (27) + (−30) (27) + (−30) Substitute: 27 for a and −30 for b. Second Edition: 2012-2013 CHAPTER 1. THE ARITHMETIC OF NUMBERS 14 In the numerator, exponents ﬁrst, then add. In the denominator, add. Finally, divide numerator by denominator. = 729 + 900 −3 Numerator, exponents ﬁrst. Denominator, add. = 1629 −3 Numerator: 729 + 900 = 1629 = −543 Divide: 1629 = −543 −3 61. Replace each occurrence of the variables a, b, c, and d with open parentheses, then substitute −42 for a, 25 for b, 26 for c, and 43 for d. ( )+( ) a+b = c−d ( )−( ) (−42) + (25) = (26) − (43) Replace variables with open parentheses. Substitute: −42 for a, 25 for b, 26 for c, and 43 for d. In the denominator, change the subtraction to adding the opposite. Next, simplify numerator and denominator, then divide. −42 + 25 26 + (−43) −17 = −17 = =1 In the denominator, add the opposite. Numerator: −42 + 25 = −17 Denominator: 26 + (−43) = −17 −17 =1 Divide: −17 63. Replace each occurrence of the variables a, b, c, and d with open parentheses, then substitute −7 for a, 48 for b, 5 for c, and 11 for d. a−b ( )−( ) = cd ( )( ) (−7) − (48) = (5) (11) Replace variables with open parentheses. Substitute: −7 for a, 48 for b, 5 for c, and 11 for d. In the numerator, change the subtraction to adding the opposite. Next, simplify numerator and denominator, then divide. −7 + (−48) (5)(11) −55 = 55 = = −1 Second Edition: 2012-2013 In the numerator, add the opposite. Numerator: −7 + (−48) = −55 Denominator: (5)(11) = 55 −55 Divide: = −1 55 1.2. ORDER OF OPERATIONS 15 65. Following Tips for Evaluating Algebraic Expressions, ﬁrst replace all occurrences of variables in the expression a2 + b2 with open parentheses, then substitute 3 for a and 4 for b and simplify. a2 + b2 = ( )2 + ( )2 2 Replace variables with open parentheses. 2 = (3) + (4) Substitute: 3 for a, 4 for b. = 9 + 16 Square: (3)2 = 9; (4)2 = 16. = 25 Add: 9 + 16 = 25. Now we deal with the second expression. (a + b)2 = (( ) + ( ))2 Replace variables with open parentheses. 2 Substitute: 3 for a, 4 for b. = ((3) + (4)) 2 = (7) Add: 3 + 4 = 7. = 49 Square: (7)2 = 49. Thus, if a = 3 and b = 4, we found that a2 + b2 = 25, but (a + b)2 = 49. Hence the expressions a2 + b2 and (a + b)2 did not produce the same results. 67. Following Tips for Evaluating Algebraic Expressions, ﬁrst replace all occurrences of variables in the expression |a||b| with open parentheses, then substitute −3 for a and 5 for b and simplify. |a||b| = |( )||( )| Replace variables with open parentheses. = |(−3)||(5)| = (3)(5) Substitute: −3 for a, 5 for b. Simplify: | − 3| = 3; |5| = 5. = 15 Multiply: (3)(5) = 15. Now we deal with the second expression. |ab| = |( )( )| Replace variables with open parentheses. = |(−3)(5)| = | − 15| Substitute: −3 for a, 5 for b. Multiply: (−3)(5) = −15. = 15 Simplify: | − 15| = 15. Thus, if a = −3 and b = 5, we found that |a||b| = 15 and |ab| = 15. Hence the expressions |a||b| and |ab| did produce the same results. 69. To evaluate the expression −236 − 324(−576 + 57), enter the expression -236-324*(-576+57) using the following keystrokes. (-) 2 3 6 − 3 2 4 × ( (-) 5 7 6 Second Edition: 2012-2013 CHAPTER 1. THE ARITHMETIC OF NUMBERS 16 + 5 ) 7 ENTER The result is shown in the following ﬁgure. Hence, −236 − 324(−576 + 57) = 167920. 71. To evaluate the expression using the following keystrokes. ( 2 7 − 0 − 270 − 900 , enter the expression (270-900)/(300-174) 300 − 174 9 1 0 7 ) 4 ÷ ) 0 ( 3 0 0 ENTER The result is shown in the following ﬁgure. Hence, 270 − 900 = −5. 300 − 174 73. First, store −93 in A with the following keystrokes. The variable A is located above the MATH button. Press the ALPHA key to access A. (-) 9 3 STO ALPHA A Second, store 84 in B with the following keystrokes. The variable B is located above the APPS button. Press the ALPHA key to access B. 8 Second Edition: 2012-2013 4 STO ALPHA B 1.2. ORDER OF OPERATIONS 17 Finally, enter the expression (A^2+B^2)/(A+B) with the following keystrokes. ( ALPHA ( A ∧ ALPHA + 2 A + ALPHA ALPHA ∧ B B ) 2 ) ÷ ENTER The results are shown in the following ﬁgure Hence, a2 + b 2 = −1745. a+b 75. Start with the formula F = (9/5)C + 32, replace the variables C with open parentheses, then substitute 60 for C and simplify. 9 Fahrenheit formula. F = C + 32 5 9 Replace C with open parentheses. = ( ) + 32 5 9 = (60) + 32 Substitute: 60 for C. 5 = 108 + 32 Multiply: (9/5)60 = 108. = 140 Add: 108 + 32 = 140. Hence, the Fahrenheit temperature is 140◦ F. 77. Start with the kinetic energy formula K = (1/2)mv 2 , replace the variables m and v with open parentheses, then substitute 7 for m and 50 for v and simplify. 1 Kinetic energy formula. K = mv 2 2 1 Replace m and v with open parentheses. = ( )( )2 2 1 = (7)(50)2 Substiute: 7 for m, 50 for v. 2 1 Square: (50)2 = 2500. = (7)(2500) 2 = 8750 Multiply: (1/2)(7)(2500) = 8750. Hence, the kinetic energy of the object is 8, 750 joules. Second Edition: 2012-2013 CHAPTER 1. THE ARITHMETIC OF NUMBERS 18 1.3 The Rational Numbers 1. The greatest common divisor of the numerator and denominator is gcd(20, 50) = 10. Divide numerator and denominator by 10. 20 20 ÷ 10 = Divide numerator and denominator 50 20 ÷ 10 by the greatest common divisor. = 2 5 Simplify. 3. The greatest common divisor of the numerator and denominator is gcd(10, 48) = 2. Divide numerator and denominator by 2. 10 10 ÷ 2 = Divide numerator and denominator 48 10 ÷ 2 by the greatest common divisor. = 5 24 Simplify. 5. The greatest common divisor of the numerator and denominator is gcd(24, 45) = 3. Divide numerator and denominator by 3. 24 24 ÷ 3 = Divide numerator and denominator 45 24 ÷ 3 by the greatest common divisor. = 8 15 Simplify. 7. Prime factor both numerator and denominator, then cancel common factors. 153 3 · 3 · 17 = Prime factorization. 170 2 · 5 · 17 3·3· 17 Cancel common factors. = 2·5· 17 3·3 = 2·5 9 = Simplify numerator and denominator. 10 9. Prime factor both numerator and denominator, then cancel common factors. 188 2 · 2 · 47 = Prime factorization. 141 3 · 47 2·2· 47 = Cancel common factors. 3· 4 7 2·2 = 3 4 = Simplify numerator and denominator. 3 Second Edition: 2012-2013 1.3. THE RATIONAL NUMBERS 19 11. Prime factor both numerator and denominator, then cancel common factors. 159 3 · 53 = 106 2 · 53 3· 5 3 = 2· 5 3 3 = 2 Prime factorization. Cancel common factors. 13. First, multiply numerators and denominators. Then prime factor the resulting numerator and denominator and cancel like factors. Simplify your ﬁnal answer. 18 20 360 · − Unlike signs yields negative answer. =− 8 13 104 2·2·2·3·3·5 =− Prime factor numerator and denominator. 2 · 2 · 2 · 13 2 ·2 ·2 ·3·3·5 =− Cancel common factors. 2· 2· 2 · 13 3·3·5 =− 13 45 Simplify numerator and denominator. =− 13 15. First, multiply numerators and denominators. Then prime factor the resulting numerator and denominator and cancel like factors. Simplify your ﬁnal answer. 18 19 342 Like signs yields positive answer. − · − = 4 13 52 2 · 3 · 3 · 19 = Prime factor numerator and denominator. 2 · 2 · 13 2 · 3 · 3 · 19 = Cancel common factors. 2 · 2 · 13 3 · 3 · 19 = 2 · 13 171 = Simplify numerator and denominator. 26 17. First, multiply numerators and denominators. Then prime factor the resulting numerator and denominator and cancel like factors. Simplify your Second Edition: 2012-2013 CHAPTER 1. THE ARITHMETIC OF NUMBERS 20 ﬁnal answer. − 16 19 304 · =− 8 6 48 2 · 2 · 2 · 2 · 19 =− 2·2·2·2·3 2· 2 · 2 · 2 · 19 =− 2 · 2 · 2 · 2 · 3 19 =− 3 Unlike signs yields negative answer. Prime factor numerator and denominator. Cancel common factors. 19. Factor the individual numerators and denominators ﬁrst, cancel common factors, then multiply numerators and denominators. Like signs gives a positive answer. 5 12 5 − · − =− 6 49 2·3 5 =− 2 · 3 5·2 = 7·7 10 = 49 2·2·3 · − 7·7 2 · 2 · 3 · − 7·7 21. Factor the individual numerators and denominators ﬁrst, cancel common factors, then multiply numerators and denominators. Unlike signs gives a negative answer. − 3·7 2·2·3 21 12 · =− · 10 55 2 · 5 5 · 11 3 · 7 2 · 2 · 3 · =− 2 · 5 5 · 11 3·7·2·3 =− 5 · 5 · 11 126 =− 275 23. Factor the individual numerators and denominators ﬁrst, cancel common factors, then multiply numerators and denominators. Unlike signs gives a negSecond Edition: 2012-2013 1.3. THE RATIONAL NUMBERS ative answer. 21 55 54 2·3·3·3 5 · 11 · − · − = 29 11 29 11 2·3·3·3 5· 11 · − = 1 1 29 5·2·3·3·3 =− 29 270 =− 29 25. First, invert and multiply. 5 58 50 50 ÷ − · − = 39 58 39 5 Factor the individual numerators and denominators ﬁrst, cancel common factors, then multiply numerators and denominators. Unlike signs gives a negative answer. 2 · 29 2·5·5 · − = 3 · 13 5 2 · 29 2 · 5 · 5 · − = 3 · 13 5 2 · 5 · 2 · 29 =− 3 · 13 580 =− 39 27. First, invert and multiply. − 60 31 60 34 ÷ =− · 17 31 17 34 Next, factor the individual numerators and denominators ﬁrst, cancel common factors, then multiply numerators and denominators. Unlike signs gives a negative answer. 2·2·3·5 · 17 2 · 2 · 3 · 5 · =− 17 2 · 3 · 5 · 31 =− 17 · 17 930 =− 289 =− 31 2 · 17 31 2 · 17 Second Edition: 2012-2013 CHAPTER 1. THE ARITHMETIC OF NUMBERS 22 29. First, invert and multiply. 7 13 28 7 − ÷ − =− · − 10 28 10 13 Factor the individual numerators and denominators ﬁrst, cancel common factors, then multiply numerators and denominators. Like signs gives a positive answer. 2·2·7 7 · − =− 2·5 13 2 · 2 · 7 7 · − =− 13 2 · 5 7·2·7 = 5 · 13 98 = 65 31. Since the denominators are diﬀerent, start by writing equivalent fractions using the least common denominator. Then add the numerators over the common denominator and simplify. 5 2 1 3 5 1 − + =− · + · 6 4 6 2 4 3 =− 3 10 + 12 12 = −10 + 3 12 = −7 12 Make equivalent fractions with LCD = 12. Simplify numerators and denominators. Add numerators over common denominator. Simplify numerator. Although this answer is perfectly acceptable, negative divided by positive gives a negative answer, so we could also write =− 7 12 33. Since the denominators are diﬀerent, start by writing equivalent fractions using the least common denominator. Then add the numerators over the comSecond Edition: 2012-2013 1.3. THE RATIONAL NUMBERS 23 mon denominator and simplify. 1 1 3 8 8 1 − + − =− · + − · 9 3 9 1 3 3 3 8 =− + − 9 9 = −8 + (−3) 9 = −11 9 Make equivalent fractions with LCD = 9. Simplify numerators and denominators. Add numerators over common denominator. Simplify numerator. Although this answer is perfectly acceptable, negative divided by positive gives a negative answer, so we could also write =− 11 9 35. First simplify by rewriting as an addition problem. Then, since the denominators are diﬀerent, write equivalent fractions using the least common denominator. Finally, add the numerators over the common denominator and simplify. 2 1 1 − − − =− 4 9 4 1 =− 4 =− + · 2 9 9 2 4 + · 9 9 4 8 9 + 36 36 = −9 + 8 36 = −1 36 Rewrite as an addition problem. Equivalent fractions with LCD = 36. Simplify numerators and denominators. Add numerators over common denominator. Simplify numerator. Although this answer is perfectly acceptable, negative divided by positive gives a negative answer, so we could also write =− 1 36 Second Edition: 2012-2013 CHAPTER 1. THE ARITHMETIC OF NUMBERS 24 37. Start by changing subtraction into addition. 8 4 8 4 − − =− + − 9 5 9 5 Add the opposite. Make equivalent fractions over a common denominator. Then add the numerators over the common denominator and simplify. 4 9 8 5 =− · + − · 9 5 5 9 36 40 =− + − 45 45 = −40 + (−36) 45 = −76 45 Make equivalent fractions with LCD = 45. Simplify numerators and denominators. Add numerators over common denominator. Simplify numerator. Although this answer is perfectly acceptable, negative divided by positive gives a negative answer, so we could also write =− 76 45 39. Evaluate the expression inside the absolute value bars ﬁrst. 8 5 2 8 5 2 − − = − + − 9 2 5 9 2 5 2 2 5 5 8 = − · + − · 9 2 5 5 2 4 8 25 = − + − 9 10 10 8 21 = − 9 10 Second Edition: 2012-2013 Add the opposite. Make equivalent fractions with LCD = 10. Add numerators over Common denominator. 1.3. THE RATIONAL NUMBERS 25 Next, take the absolute value, then make equivalent fractions with a common denominator and simplify. = = = = = 8 21 − 9 10 8 21 + − 9 10 21 9 8 10 · + − · 9 10 10 9 189 80 + − 90 90 −109 90 Take absolute value. Add the opposite. Make equivalent fractions with LCD = 90. Add. 41. First, evaluate the exponent, then multiply. 2 7 1 5 − + − − 6 2 3 1 49 5 + − = − Evaluate exponent. 36 2 3 49 5 + Multiply. = 36 6 Make equivalent fractions with a common denominator, add numerators over a common denominator and simplify. 49 36 49 = 36 79 = 36 = 1 5 6 + · 1 6 6 30 + 36 · Make equivalent fractions with LCD = 36. Add over common denominator. 43. Multiply ﬁrst, then add or subtract as needed. 8 9 9 1 − − + − 5 7 5 2 4 81 + − = Multiply. 35 5 4 7 81 1 · + − · = Make equivalent fractions 35 1 5 7 28 81 + − with LCD = 35. = 35 35 53 Add over common denominator. = 35 Second Edition: 2012-2013 26 CHAPTER 1. THE ARITHMETIC OF NUMBERS 45. Multiply ﬁrst, then add or subtract as 5 7 63 9 5 − + − =− + − 8 2 2 8 4 63 2 5 1 =− · + − · 8 1 4 2 126 5 =− + − 8 8 131 =− 8 needed. Multiply. Make equivalent fractions with LCD = 8. Add over common denominator. 47. First evaluate exponent, then multiply. 2 7 9 2 − − − 5 2 5 9 7 4 Exponent ﬁrst. = − − 5 2 25 63 4 =− − Multiply. 10 25 63 4 =− + − Add the opposite. 10 25 Make equivalent fractions with a common denominator, then add numerators over a common denominator and simplify. 4 2 63 5 Make equivalent fractions =− · + − · 10 5 25 2 8 315 + − =− with LCD = 50. 50 50 323 Add over common denominator. =− 50 49. Multiply ﬁrst, then add or subtract 6 2 8 4 6 − − = − − 5 5 9 5 45 8 6 = + 5 45 6 9 8 1 = · + · 5 9 45 1 54 8 = + 45 45 62 = 45 Second Edition: 2012-2013 as needed. Multiply. Add the opposite. Make equivalent fractions with LCD = 45. Add over common denominator. 1.3. THE RATIONAL NUMBERS 51. Multiply ﬁrst. 2 4 8 9 − − − 3 7 7 8 9 16 =− − − 21 14 9 16 =− + 21 14 27 Multiply. Add the opposite. Next, make equivalent fractions with a common denominator, add numerators over a common denominator and simplify. 16 21 32 =− 42 5 =− 42 =− 2 9 3 + · 2 14 3 27 + 42 · Make equivalent fractions with LCD = 42. Add over common denominator. 53. Replace each variable with open parentheses, then substitute −1/2 for x, −1/3 for y, and 5/2 for z. 2 xy − z 2 = ( ) ( ) − ( ) 2 5 1 1 = − − − 2 3 2 Replace variable with parentheses. Substitute −1/2 for x, −1/3 for y, and 5/2 for z. First evaluate exponent, then multiply. 1 1 25 = − Exponent ﬁrst. − − 2 3 4 1 25 = − Multiply. 6 4 1 25 = + − Add the opposite. 6 4 Make equivalent fractions with a common denominator, then add numerators over a common denominator and simplify. 1 2 25 3 = · + − · Make equivalent fractions 6 2 4 3 75 2 + − with LCD = 12. = 12 12 73 Add over common denominator. =− 12 Second Edition: 2012-2013 28 CHAPTER 1. THE ARITHMETIC OF NUMBERS 55. Replace each variable with open parentheses, then substitute 3/4 for x and −1/2 for y. 2 2 −5x2 + 2y 2 = −5 ( ) + 2 ( ) 2 2 3 1 = −5 +2 − 4 2 Exponents ﬁrst: (3/4)2 = 9/16 and (−1/2)2 = 1/4. = −5 9 16 1 +2 4 Multiply: −5(9/16) = −45/16 and 2(1/4) = 1/2 =− 45 1 + 16 2 Make equivalent fractions with LCD = 16, then add the numerators over the common denominator and simplify. 45 16 45 =− 16 −37 = 16 =− 1 1 8 + · 1 2 8 8 + 16 · 57. Replace each variable with open parentheses, then substitute 3/2 for x and −3/4 for y. 2 2 2x2 − 2xy − 3y 2 = 2 ( ) − 2 ( ) ( ) − 3 ( ) 2 2 3 3 3 3 =2 −2 − −3 − 2 2 4 4 Exponents ﬁrst: (3/2)2 = 9/4 and (−3/4)2 = 9/16. =2 9 3 9 3 −2 − −3 4 2 4 16 Multiply: 2(9/4) = 9/2, 2(3/2)(−3/4) = −9/4, and 3(9/16) = 27/16. = Second Edition: 2012-2013 9 9 27 − − − 2 4 16 1.3. THE RATIONAL NUMBERS 29 Add the opposite. 9 9 27 = + + − 2 4 16 Make equivalent fractions with LCD = 16, then add the numerators over the common denominator and simplify. 27 1 9 8 9 4 = · + · + − · 2 8 4 4 16 1 27 72 36 + + − = 16 16 16 81 = 16 59. Replace all variables with open parentheses, then substitute −1/3 for x, 1/6 for y, and 2/5 for z. x + yz = ( ) + ( ) ( ) 1 1 2 = − − 3 6 5 Replace variables with parentheses. Substitute −1/3 for x, 1/6 for y, and 2/5 for z. Multiply ﬁrst, then subtract. 1 1 =− − 3 15 1 1 =− + − 3 15 Multiply. Add the opposite. Make equivalent fractions with a common denominator, then add numerators over the common denominator and simplify. 1 1 1 5 =− · + − · 3 5 15 1 1 5 =− + − 15 15 6 =− 15 2 =− 5 Make equivalent fractions with LCD = 15. Add over common denominator. Simplify. Second Edition: 2012-2013 CHAPTER 1. THE ARITHMETIC OF NUMBERS 30 61. Replace each variable with open parentheses, then substitute 4/7 for a, 7/5 for b, and 5/2 for c. ab + bc = ( ) ( ) + ( ) ( ) 4 7 7 5 = − + − 7 5 5 2 Multiply and reduce. 28 35 + − 35 10 7 4 =− + − 5 2 =− Make equivalent fractions with LCD(5, 2) = 10, then add numerators over a common denominator and simplify. 4 2 7 5 =− · + − · 5 2 2 5 35 8 =− + − 10 10 −8 + (−35) = 10 43 =− 10 63. Replace each occurrence of the variable x with open parentheses, then substitute −1/2 for x. x3 = ( )3 3 1 = − 2 Replace variable with open parentheses. Substitute −1/2 for x. In the expression (−1/2)3 , the exponent 3 tells us to write the base −1/2 three times as a factor. 1 1 1 = − − − Write −1/2 as a 2 2 2 factor three times. 1 The product of three =− 8 negative fractions is negative. Second Edition: 2012-2013 1.3. THE RATIONAL NUMBERS 31 65. Replace all variables with open parentheses, then substitute −8/5 for x, 1/3 for y, and −8/5 for z. x − yz = ( ) − ( ) ( ) 8 8 1 = − − − 5 3 5 Replace variables with parentheses. Substitute −8/5 for x, 1/3 for y, and −8/5 for z. Multiply ﬁrst, then add or subtract as needed. 8 8 =− − − Multiply. 5 15 8 8 Add the opposite. =− + 5 15 Make equivalent fractions with a common denominator, then add numerators over the common denominator and simplify. 8 3 8 1 =− · + · 5 3 15 1 24 8 =− + 15 15 16 =− 15 Make equivalent fractions with LCD = 15. Add over common denominator. 67. Replace each occurrence of the variable x with open parentheses, then substitute −8/3 for x. Note that we must deal with the exponent ﬁrst, then negate our answer in the ﬁnal step. 2 −x2 = − ( ) 2 8 =− − 3 Replace variable with open parentheses. Substitute −8/3 for x. The exponent 2 tells us to write the base −8/3 two times as a factor. 8 8 =− − − 3 3 64 =− 9 =− 64 9 Write −8/3 as a factor two times. The product of two negative fractions is positive. Negate. Second Edition: 2012-2013 CHAPTER 1. THE ARITHMETIC OF NUMBERS 32 69. First, replace each variable with open parentheses, then substitute 7/2 for x, −5/4 for y, and −5/3 for z. 2 x2 + yz = ( ) + ( ) ( ) 2 7 5 5 = + − − 2 4 3 Replace variables with parentheses. Substitute: 7/2 for x, −5/4 for y, and −5/3 for z Next, evaluate the exponent, then multiply. 5 49 5 + − = − Evaluate exponent. 4 4 3 49 25 + Multiply. = 4 12 Make equivalent fractions with a common denominator, add numerators over a common denominator and simplify. 49 3 25 1 · + · 4 3 12 1 147 25 = + 12 12 172 = 12 43 = 3 = Make equivalent fractions with LCD = 12. Add over common denominator. Simplify. 71. The Rules Guiding Order of Operations requires that we ﬁrst perform the division. Hence: b a + b/c + d = a + + d c 73. The Rules Guiding Order of Operations requires that we attend the parentheses ﬁrst, then the division, then the addition. Hence: a + b/(c + d) = a + b c+d 75. Enter the expression 4125/1155, then press the ENTER key. Select 1:Frac from the MATH menu, then press ENTER again. The result is shown in the following ﬁgure. Second Edition: 2012-2013 1.4. DECIMAL NOTATION 33 77. Enter the expression (45/84) ∗ (70/33), then press the ENTER key. Select 1:Frac from the MATH menu, then press ENTER again. The result is shown in the following ﬁgure. Note: The parentheses are not required here, as was explained in part (b) of Example ??, but they do help emphasize the proper order of operations in this case. 79. Enter the expression (−28/33)/(−35/44), then press the ENTER key. Select 1:Frac from the MATH menu, then press ENTER again. The result is shown in the following ﬁgure. Note: The parentheses are required here, as was explained in part (c) of Example ??. 1.4 Decimal Notation 1. The two decimals are both negative. First add the magnitudes. Include trailing zeros if necessary to align the decimal points. 2.835 + 8.759 11.594 Finish by preﬁxing the common negative sign. Hence, −2.835 + (−8.759) = −11.594 Second Edition: 2012-2013 34 CHAPTER 1. THE ARITHMETIC OF NUMBERS 3. First rewrite the problem as an addition problem by adding the opposite of the second number: 19.5 − (−1.6) = 19.5 + 1.6 Then compute the sum. Include trailing zeros if necessary to align the decimal points. 19.5 + 1.6 21.1 Thus, 19.5 − (−1.6) = 19.5 + 1.6 = 21.1 5. First rewrite the problem as an addition problem by adding the opposite of the second number: −2 − 0.49 = −2 + (−0.49) In this addition problem, the decimals have like signs. Therefore, start by adding the magnitudes. Include trailing zeros if necessary to align the decimal points. 2.00 + 0.49 2.49 Finish by preﬁxing the common negative sign. Thus, −2 − 0.49 = −2 + (−0.49) = −2.49 7. Use vertical format with the unsigned numbers. Since there are a total of 3 digits to the right of the decimal point in the original numbers, the answer also has 3 digits to the right of the decimal point. 1.2 × 0.05 0.060 Like signs give a positive result. Therefore, (−1.2)(−0.05) = 0.06 Second Edition: 2012-2013 1.4. DECIMAL NOTATION 35 9. The decimals have unlike signs. First subtract the smaller magnitude from the larger magnitude. Include trailing zeros if necessary to align the decimal points. 23.49 − 0.13 23.36 Finish by preﬁxing the sign of the decimal with the larger magnitude. Hence, −0.13 + 23.49 = 23.36 11. The decimals have unlike signs. First subtract the smaller magnitude from the larger magnitude. Include trailing zeros if necessary to align the decimal points. 41.205 − 16.400 24.805 Finish by preﬁxing the sign of the decimal with the larger magnitude. Hence, 16.4 + (−41.205) = −24.805 13. First divide the magnitudes. Move the decimal point in the divisor and dividend two places to the right: 0.49 )0.45 08 Then, by long division, 0.92 49)45.08 44 1 98 98 0 Unlike signs give a negative quotient, so −0.4508 ÷ 0.49 = −0.92. Second Edition: 2012-2013 36 CHAPTER 1. THE ARITHMETIC OF NUMBERS 15. Use vertical format with the unsigned numbers. Since there are a total of 3 digits to the right of the decimal point in the original numbers, the answer also has 3 digits to the right of the decimal point. 1.42 × 3.6 852 4 26 5.112 Like signs give a positive result. Therefore, (−1.42)(−3.6) = 5.112 17. First divide the magnitudes. Move the decimal point in the divisor and dividend two places to the right: 0.24 )2.18 4 Then, by long division, 9.1 24)218.4 216 24 24 0 Unlike signs give a negative quotient, so 2.184 ÷ (−0.24) = −9.1. 19. Use vertical format with the unsigned numbers. Since there are a total of 2 digits to the right of the decimal point in the original numbers, the answer also has 2 digits to the right of the decimal point. 7.1 × 4.9 6 39 28 4 34.79 Like signs give a positive result. Therefore, (−7.1)(−4.9) = 34.79 Second Edition: 2012-2013 1.4. DECIMAL NOTATION 37 21. First divide the magnitudes. Move the decimal point in the divisor and dividend one place to the right: 9.5 )7.4 10 Then, by long division, 0.78 95)74.10 66 5 7 60 7 60 0 Unlike signs give a negative quotient, so 7.41 ÷ (−9.5) = −0.78. 23. First divide the magnitudes. Move the decimal point in the divisor and dividend one place to the right: 2.8 )24.0 8 Then, by long division, 8.6 28)240.8 224 16 8 16 8 0 Unlike signs give a negative quotient, so −24.08 ÷ 2.8 = −8.6. 25. Use vertical format with the unsigned numbers. Since there are a total of 3 digits to the right of the decimal point in the original numbers, the answer also has 3 digits to the right of the decimal point. 4.04 × 0.6 2.424 Like signs give a positive result. Therefore, (−4.04)(−0.6) = 2.424 Second Edition: 2012-2013 38 CHAPTER 1. THE ARITHMETIC OF NUMBERS 27. First rewrite the problem as an addition problem by adding the opposite of the second number: −7.2 − (−7) = −7.2 + 7 In this addition problem, the decimals have unlike signs. Therefore, start by subtracting the smaller magnitude from the larger magnitude. Include trailing zeros if necessary to align the decimal points. 7.200 − 7.000 0.200 Finish by preﬁxing the sign of the decimal with the larger magnitude. Thus, −7.2 − (−7) = −7.2 + 7 = −0.2 29. Use vertical format with the unsigned numbers. Since there are a total of 2 digits to the right of the decimal point in the original numbers, the answer also has 2 digits to the right of the decimal point. 46.9 × 0.1 4.69 Unlike signs give a negative result. Therefore, (46.9)(−0.1) = −4.69 31. Use vertical format with the unsigned numbers. Since there are a total of 2 digits to the right of the decimal point in the original numbers, the answer also has 2 digits to the right of the decimal point. 86.6 × 1.9 77 94 86 6 164.54 Unlike signs give a negative result. Therefore, (86.6)(−1.9) = −164.54 Second Edition: 2012-2013 1.4. DECIMAL NOTATION 39 33. 35. Simplify the expression inside the absolute value bars ﬁrst. − 3.49 + | − 6.9 − (−15.7)| = −3.49 + | − 6.9 + 15.7| = −3.49 + |8.8| Subtract: Add the opposite. Add: −6.9 + 15.7 = 8.8. = −3.49 + 8.8 = 5.31 Take absolute value: |8.8| = 8.8. Add: −3.49 + 8.8 = 5.31. 37. Simplify the expression inside the absolute value bars. First, add the opposite. |18.9 − 1.55| − | − 16.1 − (−17.04)| = |18.9 + (−1.55)| − | − 16.1 + 17.04| = |17.35| − |0.939999999999998| Add the opposite. Add. = 17.35 − 0.939999999999998 Take absolute value. = 16.41 Subtract. 39. Cube ﬁrst, then subtract. 8.2 − (−3.1)3 = 8.2 − (−29.791) Cube: (−3.1)3 = −29.791 = 8.2 + 29.791 = 37.991 Add the opposite. Add: 8.2 + 29.791 = 37.991. 41. First evaluate exponents, then multiply, and then subtract. 5.7 − (−8.6)(1.1)2 = 5.7 − (−8.6)(1.21) Exponents ﬁrst: 1.12 = 1.21. = 5.7 − (−10.406) = 5.7 + 10.406 Multiply: (−8.6)(1.21) = −10.406. Subtract: Add the opposite. = 16.106 Add: 5.7 + 10.406 = 16.106. Second Edition: 2012-2013 CHAPTER 1. THE ARITHMETIC OF NUMBERS 40 43. First evaluate exponents, then multiply, and then subtract. (5.67)(6.8) − (1.8)2 = (5.67)(6.8) − 3.24 = 38.556 − 3.24 Exponents ﬁrst: (1.8)2 = 3.24. Multiply: (5.67)(6.8) = 38.556. = 38.556 + (−3.24) = 35.316 Subtract: Add the opposite. Add: 38.556 + (−3.24) = 35.316. 45. Simplify the expression inside the parentheses ﬁrst. 9.6 + (−10.05 − 13.16) = 9.6 + (−10.05 + (−13.16)) Subtract: Add the opposite. = 9.6 + (−23.21) Add: −10.05 + (−13.16) = −23.21. = −13.61 Add: 9.6 + (−23.21) = −13.61. 47. Multiply ﬁrst, then add. 8.1 + 3.7(5.77) = 8.1 + 21.349 = 29.449 Multiply: 3.7(5.77) = 21.349 Add: 8.1 + 21.349 = 29.449. 49. The Rules Guiding Order of Operations tell us that we should ﬁrst evaluate the expression inside the parentheses, then divide, then add. 7.5 + 34.5/(−1.6 + 8.5) = 7.5 + 34.5/6.9 = 7.5 + 5 = 12.5 Add: −1.6 + 8.5 = 6.9 Divide: 34.5/6.9 = 5 Add: 7.5 + 5 = 12.5 51. The Rules Guiding Order of Operations tell us that we should ﬁrst evaluate the expression inside the parentheses, then divide, then add. (8.0 + 2.2)/5.1 − 4.6 = 10.2/5.1 − 4.6 = 2 − 4.6 = −2.6 Second Edition: 2012-2013 Add: 8.0 + 2.2 = 10.2 Divide: 10.2/5.1 = 2 Subtract: 2 − 4.6 = −2.6 1.4. DECIMAL NOTATION 41 53. Simplify the expression inside the absolute value bars ﬁrst. − 18.24 − | − 18.5 − 19.7| = −18.24 − | − 18.5 + (−19.7)| Subtract: Add the opposite. = −18.24 − | − 38.2| = −18.24 − 38.2 Add: −18.5 + (−19.7) = −38.2. Take absolute value: | − 38.2| = 38.2. = −18.24 + (−38.2) = −56.44 Subtract: Add the opposite. Add: −18.24 + (−38.2) = −56.44. 55. First take the absolute value, then subtract. − 4.37 − | − 8.97| = −4.37 − 8.97 = −4.37 + (−8.97) Absolute value: | − 8.97| = 8.97 Add the opposite. = −13.34 Add: −4.37 + (−8.97) = −13.34. 57. Simplify the expression inside the parentheses ﬁrst. 7.06 − (−1.1 − 4.41) = 7.06 − (−1.1 + (−4.41)) = 7.06 − (−5.51) Subtract: Add the opposite. Add: −1.1 + (−4.41) = −5.51. = 7.06 + 5.51 = 12.57 Subtract: Add the opposite. Add: 7.06 + 5.51 = 12.57. 59. Square ﬁrst, then subtract. − 2.2 − (−4.5)2 = −2.2 − 20.25 Square: (−4.5)2 = 20.25 = −2.2 + (−20.25) = −22.45 Add the opposite. Add: −2.2 + (−20.25) = −22.45. 61. Replace each variable with open parentheses, then substitute −2.9 for a and −5.4 for b. a − b2 = ( ) − ( )2 2 = (−2.9) − (−5.4) Second Edition: 2012-2013 CHAPTER 1. THE ARITHMETIC OF NUMBERS 42 Square ﬁrst, then subtract. − 2.9 − (−5.4)2 = −2.9 − 29.16 Square: (−5.4)2 = 29.16 = −2.9 + (−29.16) = −32.06 Add the opposite. Add: −2.9 + (−29.16) = −32.06. 63. Replace each variable with open parentheses, then substitute −19.55 for a, 5.62 for b, and −5.21 for c. a + |b − c| = ( ) + | ( ) − ( ) | = (−19.55) + | (5.62) − (−5.21) | Simplify the expression inside the absolute value bars ﬁrst. − 19.55 + |5.62 − (−5.21)| = −19.55 + |5.62 + 5.21| Subtract: Add the opposite. = −19.55 + |10.83| = −19.55 + 10.83 Add: 5.62 + 5.21 = 10.83. Take absolute value: |10.83| = 10.83. = −8.72 Add: −19.55 + 10.83 = −8.72. 65. Replace each variable with open parentheses, then substitute 4.3 for a, 8.5 for b, and 1.73 for c. a − bc = ( ) − ( ) ( ) = (4.3) − (8.5) (1.73) Multiply ﬁrst, then subtract. 4.3 − 8.5(1.73) = 4.3 − 14.705 = 4.3 + (−14.705) Multiply: 8.5(1.73) = 14.705 Add the opposite. = −10.405 Add: 4.3 + (−14.705) = −10.405. 67. Replace each variable with open parentheses, then substitute −7.36 for a, −17.6 for b, and −19.07 for c. a − (b − c) = ( ) − (( ) − ( )) = (−7.36) − ((−17.6) − (−19.07)) Second Edition: 2012-2013 1.4. DECIMAL NOTATION 43 Simplify the expression inside the parentheses ﬁrst. − 7.36 − (−17.6 − (−19.07)) = −7.36 − (−17.6 + 19.07) = −7.36 − 1.47 Subtract: Add the opposite. Add: −17.6 + 19.07 = 1.47. = −7.36 + (−1.47) = −8.83 Subtract: Add the opposite. Add: −7.36 + (−1.47) = −8.83. 69. Replace each variable with open parentheses, then substitute 4.7 for a, 54.4 for b, 1.7 for c, and 5.1 for d.. a + b/(c + d) = ( ) + ( ) / (( ) + ( )) = (4.7) + (54.4) / ((1.7) + (5.1)) The Rules Guiding Order of Operations tell us that we should ﬁrst evaluate the expression inside the parentheses, then divide, then add. 4.7 + 54.4/(1.7 + 5.1) = 4.7 + 54.4/6.8 Add: 1.7 + 5.1 = 6.8 = 4.7 + 8 = 12.7 Divide: 54.4/6.8 = 8 Add: 4.7 + 8 = 12.7 71. Replace each variable with open parentheses, then substitute −2.45 for a, 5.6 for b, and −3.2 for c. 2 ab − c2 = ( ) ( ) − ( ) 2 = (−2.45) (5.6) − (−3.2) First evaluate exponents, then multiply, and then subtract. (−2.45)(5.6) − (−3.2)2 = (−2.45)(5.6) − 10.24 Exponents ﬁrst: (−3.2)2 = 10.24. = −13.72 − 10.24 Multiply: (−2.45)(5.6) = −13.72. = −13.72 + (−10.24) = −23.96 Subtract: Add the opposite. Add: −13.72 + (−10.24) = −23.96. 73. Replace each variable with open parentheses, then substitute −4.9 for a and −2.67 for b. a − |b| = ( ) − | ( ) | = (−4.9) − | (−2.67) | Second Edition: 2012-2013 CHAPTER 1. THE ARITHMETIC OF NUMBERS 44 First take the absolute value, then subtract. − 4.9 − | − 2.67| = −4.9 − 2.67 Absolute value: | − 2.67| = 2.67 = −4.9 + (−2.67) = −7.57 Add the opposite. Add: −4.9 + (−2.67) = −7.57. 75. First, store 1.25 in the variable X with the following keystrokes. . 1 2 5 STO X,T,θ,n ENTER Next, enter the expression 3.5 − 1.7x with the following keystrokes. 3 . 5 − . 1 7 × X,T,θ,n ENTER The results are shown below. Thus, the answer is approximately 1.375. We now need to round this answer to the nearest tenth. Mark the rounding digit in the tenths place and the test digit to its immediate right. Test digit 1. 3 7 5 Rounding digit Because the test digit is greater than or equal to 5, add 1 to the rounding digit, then replace all digits to the right of the rounding digit with zeros. 1.375 ≈ 1.400 Delete the trailing zeros from the end of the fractional part of a decimal. This does not change our answer’s value. 1.375 ≈ 1.4 Therefore, if x = 1.25. then to the nearest tenth: 3.5 − 1.7x ≈ 1.4 Second Edition: 2012-2013 1.4. DECIMAL NOTATION 45 77. First, store 2.86 in the variable X with the following keystrokes. . 2 8 6 STO X,T,θ,n ENTER Next, enter the expression 1.7x2 − 3.2x + 4.5 with the following keystrokes. 1 . 7 × X,T,θ,n + ∧ . 4 − 2 5 3 . 2 × X,T,θ,n ENTER The results are shown below. Thus, the answer is approximately 9.25332. We now need to round this answer to the nearest hundredth. Mark the rounding digit in the hundredths place and the test digit to its immediate right. Test digit 9.2 5 3 32 Rounding digit Because the test digit is less than 5, leave the rounding digit alone, then replace all digits to the right of the rounding digit with zeros. 9.25332 ≈ 9.25000 Delete the trailing zeros from the end of the fractional part of a decimal. This does not change our answer’s value. 9.25332 ≈ 9.25 Therefore, if x = 2.86. then to the nearest hundredth: 1.7x2 − 3.2x + 4.5 ≈ 9.25 Second Edition: 2012-2013 CHAPTER 1. THE ARITHMETIC OF NUMBERS 46 79. First, store −1.27 in the variable X with the following keystrokes. (-) . 1 2 7 X,T,θ,n STO ENTER Next, enter the expression −18.6 + 4.4x2 − 3.2x3 with the following keystrokes. (-) 1 8 3 . + 6 . 4 × 2 . X,T,θ,n 4 ∧ × X,T,θ,n 3 ∧ 2 − ENTER The results are shown below. Thus, the answer is approximately −4.9484144. We now need to round this answer to the nearest thousandth. Mark the rounding digit in the thousandths place and the test digit to its immediate right. Test digit −4.94 8 4 144 Rounding digit Because the test digit is less than 5, keep the rounding digit the same, then replace all digits to the right of the rounding digit with zeros. −4.9484144 ≈ −4.9480000 Delete the trailing zeros from the end of the fractional part of a decimal. This does not change our answer’s value. −4.9484144 ≈ −4.948 Therefore, if x = −1.27. then to the nearest thousandth: −18.6 + 4.4x2 − 3.2x3 ≈ −4.948 Second Edition: 2012-2013 1.5. ALGEBRAIC EXPRESSIONS 1.5 47 Algebraic Expressions 1. Use the associative property to regroup, then simplify. −3(6a) = ((−3) · 6)a = −18a Apply the associative property. Simplify. 3. Use the associative property to regroup, then simplify. −9(6ab) = ((−9) · 6)ab = −54ab Apply the associative property. Simplify. 5. Use the associative property to regroup, then simplify. −7(3x2 ) = ((−7) · 3)x2 2 = −21x Apply the associative property. Simplify. 7. Use the distributive property to expand the expression, and then use order of operations to simplify. 4(3x − 7y) = 4(3x) − 4(7y) = 12x − 28y Apply the distributive property. Simplify. 9. Use the distributive property to expand the expression, and then use order of operations to simplify. −6(−y + 9) = −6(−y) + (−6)(9) = 6y − 54 Apply the distributive property. Simplify. 11. Use the distributive property to expand the expression, and then use order of operations to simplify. −9(s + 9) = −9(s) + (−9)(9) = −9s − 81 Apply the distributive property. Simplify. 13. To negate a sum, simply negate each term of the sum: −(−3u − 6v + 8) = 3u + 6v − 8 Second Edition: 2012-2013 48 CHAPTER 1. THE ARITHMETIC OF NUMBERS 15. Use the distributive property to expand the expression, and then use order of operations to simplify. −8(4u2 − 6v 2 ) = −8(4u2 ) − (−8)(6v 2 ) 2 = −32u + 48v 2 Apply the distributive property. Simplify. 17. To negate a sum, simply negate each term of the sum: −(7u + 10v + 8) = −7u − 10v − 8 19. First use the distributive property to factor out the common variable part. Then simplify. −19x + 17x − 17x = (−19 + 17 − 17)x = −19x Distributive property. Simplify. 21. First use the distributive property to factor out the common variable part. Then simplify. 14x3 − 10x3 = (14 − 10)x3 3 = 4x Distributive property. Simplify. 23. First use the distributive property to factor out the common variable part. Then simplify. 9y 2 x + 13y 2 x − 3y 2 x = (9 + 13 − 3)y 2 x 2 = 19y x Distributive property. Simplify. 25. First use the distributive property to factor out the common variable part. Then simplify. 15m + 14m = (15 + 14)m = 29m Distributive property. Simplify. 27. Combine like terms and write down the answer. 9 − 17m − m + 7 = 16 − 18m Hint: 9 + 7 = 16 and −17m − m = −18m. Second Edition: 2012-2013 1.5. ALGEBRAIC EXPRESSIONS 49 29. Combine like terms and write down the answer. −6y 2 − 3x3 + 4y 2 + 3x3 = −2y 2 Hint: −6y 2 + 4y 2 = −2y 2 and −3x3 + 3x3 = 0. 31. Combine like terms and write down the answer. −5m − 16 + 5 − 20m = −25m − 11 Hint: −5m − 20m = −25m and −16 + 5 = −11. 33. Combine like terms and write down the answer. −16x2 y + 7y 3 − 12y 3 − 12x2 y = −28x2 y − 5y 3 Hint: −16x2 y − 12x2 y = −28x2 y and 7y 3 − 12y 3 = −5y 3 . 35. Combine like terms and write down the answer. −14r + 16 − 7r − 17 = −21r − 1 Hint: −14r − 7r = −21r and 16 − 17 = −1. 37. Combine like terms and write down the answer. 14 − 16y − 10 − 13y = 4 − 29y Hint: 14 − 10 = 4 and −16y − 13y = −29y. 39. Use the distributive property to expand the expression. Then combine like terms mentally. 3 − (−5y + 1) = 3 + 5y − 1 = 2 + 5y Distribute (negate the sum). Combine like terms. 41. Use the distributive property to expand the expression. Then combine like terms mentally. − (9y 2 + 2x2 ) − 8(5y 2 − 6x2 ) = −9y 2 − 2x2 − 40y 2 + 48x2 2 2 = −49y + 46x Distribute. Combine like terms. Second Edition: 2012-2013 CHAPTER 1. THE ARITHMETIC OF NUMBERS 50 43. Use the distributive property to expand the expression. Then combine like terms mentally. 2(10 − 6p) + 10(−2p + 5) = 20 − 12p − 20p + 50 = 70 − 32p Distribute. Combine like terms. 45. Use the distributive property to expand the expression. Then combine like terms mentally. 4(−10n + 5) − 7(7n − 9) = −40n + 20 − 49n + 63 = −89n + 83 Distribute. Combine like terms. 47. Use the distributive property to expand the expression. Then combine like terms mentally. −4x − 4 − (10x − 5) = −4x − 4 − 10x + 5 = −14x + 1 Distribute (negate the sum). Combine like terms. 49. First use the distributive property to expand the expression. Then rearrange the terms and combine like terms. −7 − (5 + 3x) = −7 − 5 − 3x = −12 − 3x Distribute (negate the sum). Combine like terms. 51. Use the distributive property to expand the expression. Then combine like terms mentally. −8(−5y − 8) − 7(−2 + 9y) = 40y + 64 + 14 − 63y = −23y + 78 Distribute. Combine like terms. 53. Use the distributive property to expand the expression. Then combine like terms mentally. 4(−7y 2 − 9x2 y) − 6(−5x2 y − 5y 2 ) = −28y 2 − 36x2 y + 30x2 y + 30y 2 2 2 = 2y − 6x y Distribute. Combine like terms. 55. Use the distributive property to expand the expression. Then combine like terms mentally. 6s − 7 − (2 − 4s) = 6s − 7 − 2 + 4s = 10s − 9 Second Edition: 2012-2013 Distribute (negate the sum). Combine like terms. 1.5. ALGEBRAIC EXPRESSIONS 51 57. Use the distributive property to expand the expression. Then combine like terms mentally. 9(9 − 10r) + (−8 − 2r) = 81 − 90r − 8 − 2r = 73 − 92r Distribute. Combine like terms. 59. We analyze the expression inside the parentheses ﬁrst. Multiply ﬁrst, distributing the −5. −7x + 7[2x − 5[8x + 5]] = −7x + 7(2x − 40x − 25) = −7x + 7(−38x − 25) Next, distribute 7 and simplify. = −7x − 266x − 175 = −273x − 175 61. We analyze the expression inside the parentheses ﬁrst. Multiply ﬁrst, distributing the 2. 6x − 4[−3x + 2[5x − 7]] = 6x − 4(−3x + 10x − 14) = 6x − 4(7x − 14) Next, distribute −4 and simplify. = 6x − 28x + 56 = −22x + 56 63. We analyze the expression inside the parentheses ﬁrst. Multiply ﬁrst, distributing the −3. −8x − 5[2x − 3[−4x + 9]] = −8x − 5(2x + 12x − 27) = −8x − 5(14x − 27) Next, distribute −5 and simplify. = −8x − 70x + 135 = −78x + 135 Second Edition: 2012-2013 Chapter 2 Solving Linear Equations 2.1 Solving Equations: One Step 1. Substitute 2 for x in the equation, then simplify both sides of the resulting equation. x+2=4 Original equation. 2+2=4 Substitute 2 for x. 4=4 Simplify both sides. This last equation is a true statement. Hence, 2 is a solution of the equation x + 2 = 4. For contrast, substitute 3 for x in the equation and simplify. x+2=4 Original equation. 3+2=4 5=4 Substitute 3 for x. Simplify both sides. This last equation is not a true statement. Hence, 3 is not a solution of x + 2 = 4. Readers should check that the remaining two given numbers are not solutions by substituting them into the equation and showing that a false statement results. 3. Substitute 13 for x in the equation, then simplify both sides of the resulting equation. x−9=4 13 − 9 = 4 Original equation. Substitute 13 for x. 4=4 Simplify both sides. 53 CHAPTER 2. SOLVING LINEAR EQUATIONS 54 This last equation is a true statement. Hence, 13 is a solution of the equation x − 9 = 4. For contrast, substitute 14 for x in the equation and simplify. x−9=4 14 − 9 = 4 Original equation. Substitute 14 for x. 5=4 Simplify both sides. This last equation is not a true statement. Hence, 14 is not a solution of x − 9 = 4. Readers should check that the remaining two given numbers are not solutions by substituting them into the equation and showing that a false statement results. 5. Substitute 9 for x in the equation, then simplify both sides of the resulting equation. x−3= 6 9−3= 6 6=6 Original equation. Substitute 9 for x. Simplify both sides. This last equation is a true statement. Hence, 9 is a solution of the equation x − 3 = 6. For contrast, substitute 10 for x in the equation and simplify. x−3=6 10 − 3 = 6 Original equation. Substitute 10 for x. 7=6 Simplify both sides. This last equation is not a true statement. Hence, 10 is not a solution of x − 3 = 6. Readers should check that the remaining two given numbers are not solutions by substituting them into the equation and showing that a false statement results. 7. The number −6 is the only solution of the equation x − 1 = −7. Similarly, −8 is the only solution of the equation x = −8. Therefore x − 1 = −7 and x = −8 do not have the same solution sets and are not equivalent. 9. The number 0 is the only solution of the equation x − 5 = −5. Similarly, 0 is the only solution of the equation x = 0. Therefore x − 5 = −5 and x = 0 have the same solution sets and are equivalent. 11. By inspection, the equation x2 = 1 has two solutions, −1 and 1. On the other hand, the equation x = 1 has a single solution, namely 1. Hence the equations x2 = 1 and x = 1 do not have the same solution sets and are not equivalent. Second Edition: 2012-2013 2.1. SOLVING EQUATIONS: ONE STEP 55 13. To undo the eﬀect of subtracting 20, add 20 to both sides of the equation. x − 20 = 9 x − 20 + 20 = 9 + 20 x = 29 Original equation. Add 20 to both sides. On the left, adding 20 “undoes” the eﬀect of subtracting 20 and returns x. On the right, 9 + 20 = 29. Hence, 29 is a solution of x − 20 = 9. 15. To undo the eﬀect of subtracting 3, add 3 to both sides of the equation. 16 = x − 3 16 + 3 = x − 3 + 3 19 = x Original equation. Add 3 to both sides. On the right, adding 3 “undoes” the eﬀect of subtracting 3 and returns x. On the left, 16 + 3 = 19. Hence, 19 is a solution of 16 = x − 3. 17. To undo the eﬀect of adding 11, subtract 11 from both sides of the equation. x + 11 = 20 x + 11 − 11 = 20 − 11 x=9 Original equation. Subtract 11 from both sides. On the left, subtracting 11 “undoes” the eﬀect of adding 11 and returns x. On the right, 20 − 11 = 9. Hence, 9 is a solution of x + 11 = 20. 19. To undo the eﬀect of subtracting 19, add 19 to both sides of the equation. 9 = x − 19 9 + 19 = x − 19 + 19 28 = x Original equation. Add 19 to both sides. On the right, adding 19 “undoes” the eﬀect of subtracting 19 and returns x. On the left, 9 + 19 = 28. Hence, 28 is a solution of 9 = x − 19. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 56 21. To undo the eﬀect of adding 9, subtract 9 from both sides of the equation. 20 = 9 + x 20 − 9 = 9 + x − 9 11 = x Original equation. Subtract 9 from both sides. On the right, subtracting 9 “undoes” the eﬀect of adding 9 and returns x. On the left, 20 − 9 = 11. Hence, 11 is a solution of 20 = 9 + x. 23. To undo the eﬀect of adding 17, subtract 17 from both sides of the equation. 18 = 17 + x 18 − 17 = 17 + x − 17 1=x Original equation. Subtract 17 from both sides. On the right, subtracting 17 “undoes” the eﬀect of adding 17 and returns x. On the left, 18 − 17 = 1. Hence, 1 is a solution of 18 = 17 + x. 25. To undo the eﬀect of adding 7, subtract 7 from both sides of the equation. 7 + x = 19 7 + x − 7 = 19 − 7 x = 12 Original equation. Subtract 7 from both sides. On the left, subtracting 7 “undoes” the eﬀect of adding 7 and returns x. On the right, 19 − 7 = 12. Hence, 12 is a solution of 7 + x = 19. 27. To undo the eﬀect of subtracting 9, add 9 to both sides of the equation. x−9=7 x−9+9=7+9 x = 16 Original equation. Add 9 to both sides. On the left, adding 9 “undoes” the eﬀect of subtracting 9 and returns x. On the right, 7 + 9 = 16. Hence, 16 is a solution of x − 9 = 7. Second Edition: 2012-2013 2.1. SOLVING EQUATIONS: ONE STEP 57 29. To undo the eﬀect of adding 15, subtract 15 from both sides of the equation. x + 15 = 19 x + 15 − 15 = 19 − 15 x=4 Original equation. Subtract 15 from both sides. On the left, subtracting 15 “undoes” the eﬀect of adding 15 and returns x. On the right, 19 − 15 = 4. Hence, 4 is a solution of x + 15 = 19. 31. To undo the eﬀect of adding 10, subtract 10 from both sides of the equation. 10 + x = 15 10 + x − 10 = 15 − 10 x=5 Original equation. Subtract 10 from both sides. On the left, subtracting 10 “undoes” the eﬀect of adding 10 and returns x. On the right, 15 − 10 = 5. Hence, 5 is a solution of 10 + x = 15. 33. To undo the eﬀects of subtracting 4/9, ﬁrst add 4/9 to both sides of the equation. Then make equivalent fractions with a common denominator and simplify. 4 2 = 9 7 4 4 2 4 x− + = + 9 9 7 9 18 28 + x= 63 63 x− x= 46 63 Original equation. Add 4/9 to both sides. On the left, adding 4/9 “undoes” the eﬀect of subtracting 4/9 and returns x. On the right, make equivalent fractions with a common denominator. Simplify. 35. To undo the eﬀects of adding 7/4, ﬁrst subtract 7/4 from both sides of the equation. Then make equivalent fractions with a common denominator and Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 58 simplify. 7 4 =− 4 9 7 7 4 7 x+ − =− − 4 4 9 4 16 63 x=− − 36 36 x+ −79 36 x= Original equation. Subtract 7/4 from both sides. On the left, subtracting 7/4 “undoes” the eﬀect of adding 7/4 and returns x. On the right, make equivalent fractions with a common denominator. Simplify. 37. To undo the eﬀects of adding 5/9, ﬁrst subtract 5/9 from both sides of the equation. Then make equivalent fractions with a common denominator and simplify. 5 7 = 9 2 5 5 7 5 x+ − = − 9 9 2 9 63 10 x= − 18 18 x+ x= 53 18 Original equation. Subtract 5/9 from both sides. On the left, subtracting 5/9 “undoes” the eﬀect of adding 5/9 and returns x. On the right, make equivalent fractions with a common denominator. Simplify. 39. To undo the eﬀects of subtracting 9/8, ﬁrst add 9/8 to both sides of the equation. Then make equivalent fractions with a common denominator and simplify. 9 1 =− 8 2 9 9 1 9 x− + =− + 8 8 2 8 4 9 x=− + 8 8 x− x= 5 8 Second Edition: 2012-2013 Original equation. Add 9/8 to both sides. On the left, adding 9/8 “undoes” the eﬀect of subtracting 9/8 and returns x. On the right, make equivalent fractions with a common denominator. Simplify. 2.1. SOLVING EQUATIONS: ONE STEP 59 41. To undo multiplying by −5.1, divide both sides of the equation by −5.1. −5.1x = −12.75 −5.1x −12.75 = −5.1 −5.1 x = 2.5 Original equation. Divide both sides by −5.1. Simplify: −12.75/(−5.1) = 2.5. 43. To undo multiplying by −6.9, divide both sides of the equation by −6.9. −6.9x = −58.65 −6.9x −58.65 = −6.9 −6.9 x = 8.5 Original equation. Divide both sides by −6.9. Simplify: −58.65/(−6.9) = 8.5. 45. To undo multiplying by −3.6, divide both sides of the equation by −3.6. −3.6x = −24.12 −3.6x −24.12 = −3.6 −3.6 x = 6.7 Original equation. Divide both sides by −3.6. Simplify: −24.12/(−3.6) = 6.7. 47. To undo the eﬀect of dividing by 2, multiply both sides of the equation by 2. x = −11 x 2 2 = 2 (−11) 2 x = −22 Original equation. Multiply both sides by 2. On the left, simplify. On the right, multiply: 2(−11) = −22. 49. To undo the eﬀect of dividing by 8, multiply both sides of the equation by 8. x = −18 x 8 8 = 8 (−18) 8 x = −144 Original equation. Multiply both sides by 8. On the left, simplify. On the right, multiply: 8(−18) = −144. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 60 51. To undo the eﬀect of dividing by −7, multiply both sides of the equation by −7. x = 15 −7 x −7 = −7 (15) −7 x = −105 2.2 Original equation. Multiply both sides by −7. On the left, simplify. On the right, multiply: −7(15) = −105. Solving Equations: Multiple Steps 1. On the left, order of operations demands that we ﬁrst multiply x by 2, then subtract 20. To solve this equation for x, we must “undo” each of these operations in inverse order. Thus, we will ﬁrst add 20 to both sides of the equation, then divide both sides of the resulting equation by 2. 2x − 20 = −12 2x − 20 + 20 = −12 + 20 Original equation. To “undo” subtracting 20, add 20 to both sides of the equation. 2x = 8 8 2x = 2 2 Simplify both sides. x=4 Simplify both sides. To “undo” multiplying by 2, divide both sides of the equation by 2. 3. On the left, order of operations demands that we ﬁrst multiply x by 3, then add −11. To solve this equation for x, we must “undo” each of these operations in inverse order. Thus, we will ﬁrst add 11 to both sides of the equation, then divide both sides of the resulting equation by 3. −11 + 3x = −44 −11 + 3x + 11 = −44 + 11 3x = −33 −33 3x = 3 3 x = −11 Second Edition: 2012-2013 Original equation. To “undo” adding −11, add 11 to both sides of the equation. Simplify both sides. To “undo” multiplying by 3, divide both sides of the equation by 3. Simplify both sides. 2.2. SOLVING EQUATIONS: MULTIPLE STEPS 61 5. On the left, order of operations demands that we ﬁrst multiply x by −5, then add 17. To solve this equation for x, we must “undo” each of these operations in inverse order. Thus, we will ﬁrst subtract 17 from both sides of the equation, then divide both sides of the resulting equation by −5. −5x + 17 = 112 −5x + 17 − 17 = 112 − 17 −5x = 95 −5x 95 = −5 −5 x = −19 7. On the left, order then subtract 14. To operations in inverse equation, then divide Original equation. To “undo” adding 17, subtract 17 from both sides of the equation. Simplify both sides. To “undo” multiplying by −5, divide both sides of the equation by −5. Simplify both sides. of operations demands that we ﬁrst multiply x by −16, solve this equation for x, we must “undo” each of these order. Thus, we will ﬁrst add 14 to both sides of the both sides of the resulting equation by −16. −16x − 14 = 2 −16x − 14 + 14 = 2 + 14 −16x = 16 16 −16x = −16 −16 x = −1 Original equation. To “undo” subtracting 14, add 14 to both sides of the equation. Simplify both sides. To “undo” multiplying by −16, divide both sides of the equation by −16. Simplify both sides. 9. On the left, order of operations demands that we ﬁrst multiply x by −13, then add 5. To solve this equation for x, we must “undo” each of these operations in inverse order. Thus, we will ﬁrst subtract 5 from both sides of the equation, then divide both sides of the resulting equation by −13. 5 − 13x = 70 5 − 13x − 5 = 70 − 5 −13x = 65 65 −13x = −13 −13 x = −5 Original equation. To “undo” adding 5, subtract 5 from both sides of the equation. Simplify both sides. To “undo” multiplying by −13, divide both sides of the equation by −13. Simplify both sides. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 62 11. On the left, order of operations demands that we ﬁrst multiply x by −9, then add −2. To solve this equation for x, we must “undo” each of these operations in inverse order. Thus, we will ﬁrst add 2 to both sides of the equation, then divide both sides of the resulting equation by −9. −2 − 9x = −74 −2 − 9x + 2 = −74 + 2 −9x = −72 −9x −72 = −9 −9 x=8 Original equation. To “undo” adding −2, add 2 to both sides of the equation. Simplify both sides. To “undo” multiplying by −9, divide both sides of the equation by −9. Simplify both sides. 13. On the left, order of operations demands that we ﬁrst multiply x by −1, then add 7. To solve this equation for x, we must “undo” each of these operations in inverse order. Thus, we will ﬁrst subtract 7 from both sides of the equation, then divide both sides of the resulting equation by −1. 7 − x = −7 7 − x − 7 = −7 − 7 −1x = −14 −14 −1x = −1 −1 x = 14 Original equation. To “undo” adding 7, subtract 7 from both sides of the equation. Simplify both sides. To “undo” multiplying by −1, divide both sides of the equation by −1. Simplify both sides. 15. On the left, order of operations demands that we ﬁrst multiply x by −4, then add 14. To solve this equation for x, we must “undo” each of these operations in inverse order. Thus, we will ﬁrst subtract 14 from both sides of the equation, then divide both sides of the resulting equation by −4. −4x + 14 = 74 −4x + 14 − 14 = 74 − 14 −4x = 60 60 −4x = −4 −4 x = −15 Second Edition: 2012-2013 Original equation. To “undo” adding 14, subtract 14 from both sides of the equation. Simplify both sides. To “undo” multiplying by −4, divide both sides of the equation by −4. Simplify both sides. 2.2. SOLVING EQUATIONS: MULTIPLE STEPS 63 17. On the left, order of operations demands that we ﬁrst divide x by 7, then subtract 1/3. To solve this equation for x, we must “undo” each of these operations in inverse order. Thus, we will ﬁrst add 1/3 to both sides of the equation, then multiply both sides of the resulting equation by 7. x 1 9 − =− 7 3 8 x 1 1 9 1 − + =− + 7 3 3 8 3 x 27 8 =− + 7 24 24 x 19 =− 7 24 x 19 7 = − 7 7 24 x=− 133 24 Original equation. To “undo” subtracting 1/3, add 1/3 to both sides of the equation. On the left, simplify. On the right, make equivalent fractions with a common denominator. 27 8 19 Add: − + =− . 24 24 24 To “undo” dividing by 7, multiply both sides of the equation by 7. On the left, simplify. On the right, 19 133 . multiply: − 7=− 24 24 19. On the left, order of operations demands that we ﬁrst divide x by 7, then add 4/9. To solve this equation for x, we must “undo” each of these operations in inverse order. Thus, we will ﬁrst subtract 4/9 from both sides of the equation, then multiply both sides of the resulting equation by 7. x 4 3 + = 7 9 2 x 4 4 3 4 + − = − 7 9 9 2 9 27 8 x = − 7 18 18 19 x = 7 18 x 19 7 = 7 7 18 x= 133 18 Original equation. To “undo” adding 4/9, subtract 4/9 from both sides of the equation. On the left, simplify. On the right, make equivalent fractions with a common denominator. 27 8 19 Subtract: − = . 18 18 18 To “undo” dividing by 7, multiply both sides of the equation by 7. On the left, simplify. On the right, 19 133 . multiply: 7= 18 18 Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 64 21. On the left, order of operations demands that we ﬁrst divide x by 2, then add 2/3. To solve this equation for x, we must “undo” each of these operations in inverse order. Thus, we will ﬁrst subtract 2/3 from both sides of the equation, then multiply both sides of the resulting equation by 2. x 2 4 + = 2 3 7 x 2 2 4 2 + − = − 2 3 3 7 3 x 12 14 = − 2 21 21 x 2 =− 2 21 x 2 2 = − 2 2 21 x=− 4 21 Original equation. To “undo” adding 2/3, subtract 2/3 from both sides of the equation. On the left, simplify. On the right, make equivalent fractions with a common denominator. 12 14 2 Subtract: − =− . 21 21 21 To “undo” dividing by 2, multiply both sides of the equation by 2. On the left, simplify. On the right, 2 4 multiply: − 2=− . 21 21 23. On the left, order of operations demands that we ﬁrst divide x by 5, then subtract 9/2. To solve this equation for x, we must “undo” each of these operations in inverse order. Thus, we will ﬁrst add 9/2 to both sides of the equation, then multiply both sides of the resulting equation by 5. x 9 5 − =− 5 2 3 x 9 9 5 9 − + =− + 5 2 2 3 2 10 27 x =− + 5 6 6 17 x = 5 6 x 17 5 = 5 5 6 x= 85 6 Second Edition: 2012-2013 Original equation. To “undo” subtracting 9/2, add 9/2 to both sides of the equation. On the left, simplify. On the right, make equivalent fractions with a common denominator. 10 27 17 Add: − + = . 6 6 6 To “undo” dividing by 5, multiply both sides of the equation by 5. On the left, simplify. On the right, 17 85 . multiply: 5= 6 6 2.2. SOLVING EQUATIONS: MULTIPLE STEPS 65 25. On the left, order of operations demands that we ﬁrst multiply x by 0.3, then add 1.7. To solve this equation for x, we must “undo” each of these operations in inverse order. Thus, we will ﬁrst subtract 1.7 from both sides of the equation, then divide both sides by 0.3. 0.3x + 1.7 = 3.05 0.3x + 1.7 − 1.7 = 3.05 − 1.7 0.3x = 1.35 0.3x 1.35 = 0.3 0.3 x = 4.5 Original equation. To “undo” adding 1.7, subtract 1.7 from both sides. On the left, simplify. On the right, subtract: 3.05 − 1.7 = 1.35. To “undo” multiplying by 0.3, divide both sides by 0.3. On the left, simplify. On the right, divide: 1.35/0.3 = 4.5. 27. On the left, order of operations demands that we ﬁrst multiply x by 1.2, then add 5.2. To solve this equation for x, we must “undo” each of these operations in inverse order. Thus, we will ﬁrst subtract 5.2 from both sides of the equation, then divide both sides by 1.2. 1.2x + 5.2 = 14.92 1.2x + 5.2 − 5.2 = 14.92 − 5.2 1.2x = 9.72 9.72 1.2x = 1.2 1.2 x = 8.1 Original equation. To “undo” adding 5.2, subtract 5.2 from both sides. On the left, simplify. On the right, subtract: 14.92 − 5.2 = 9.72. To “undo” multiplying by 1.2, divide both sides by 1.2. On the left, simplify. On the right, divide: 9.72/1.2 = 8.1. 29. On the left, order of operations demands that we ﬁrst multiply x by 3.5, then subtract 3.7. To solve this equation for x, we must “undo” each of these operations in inverse order. Thus, we will ﬁrst add 3.7 to both sides of the Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 66 equation, then divide both sides by 3.5. 3.5x − 3.7 = −26.10 3.5x − 3.7 + 3.7 = −26.10 + 3.7 3.5x = −22.4 3.5x −22.4 = 3.5 3.5 x = −6.4 Original equation. To “undo” subtracting 3.7, add 3.7 to both sides. On the left, simplify. On the right, add: −26.10 + 3.7 = −22.4. To “undo” multiplying by 3.5, divide both sides by 3.5. On the left, simplify. On the right, divide: −22.4/3.5 = −6.4. 31. On the left, order of operations demands that we ﬁrst multiply x by −4.7, then subtract 7.4. To solve this equation for x, we must “undo” each of these operations in inverse order. Thus, we will ﬁrst add 7.4 to both sides of the equation, then divide both sides by −4.7. −4.7x − 7.4 = −48.29 −4.7x − 7.4 + 7.4 = −48.29 + 7.4 −4.7x = −40.89 −40.89 −4.7x = −4.7 −4.7 x = 8.7 Original equation. To “undo” subtracting 7.4, add 7.4 to both sides. On the left, simplify. On the right, add: −48.29 + 7.4 = −40.89. To “undo” multiplying by −4.7, divide both sides by −4.7. On the left, simplify. On the right, divide: −40.89/ − 4.7 = 8.7. 33. We need to isolate all terms containing x on one side of the equation. We can eliminate −5x from the right-hand side of 13 − 9x = 11 − 5x by adding 5x to both sides of the equation. 13 − 9x = 11 − 5x 13 − 9x + 5x = 11 − 5x + 5x −4x + 13 = 11 Original equation. Add 5x to both sides. Simplify both sides. Next, eliminate 13 from the left-hand side of the last equation by subtracting 13 from both sides of the equation. −4x + 13 − 13 = 11 − 13 −4x = −2 Second Edition: 2012-2013 Subtract 13 both sides. Simplify both sides. 2.2. SOLVING EQUATIONS: MULTIPLE STEPS 67 Note how we have isolated all terms containing x on one side of the equation. Finally, to “undo” multiplying by −4, divide both sides of the equation by −4. −4x −2 = −4 −4 1 x= 2 Divide both sides by −4. Reduce to lowest terms. 35. We need to isolate all terms containing x on one side of the equation. We can eliminate 19x from the right-hand side of 11x + 10 = 19x + 20 by subtracting 19x from both sides of the equation. 11x + 10 = 19x + 20 11x + 10 − 19x = 19x + 20 − 19x −8x + 10 = 20 Original equation. Subtract 19x from both sides. Simplify both sides. Next, eliminate 10 from the left-hand side of the last equation by subtracting 10 from both sides of the equation. −8x + 10 − 10 = 20 − 10 −8x = 10 Subtract 10 both sides. Simplify both sides. Note how we have isolated all terms containing x on one side of the equation. Finally, to “undo” multiplying by −8, divide both sides of the equation by −8. 10 −8x = −8 −8 5 x=− 4 Divide both sides by −8. Reduce to lowest terms. 37. We need to isolate all terms containing x on one side of the equation. We can eliminate −19x from the right-hand side of 11 − 15x = 13 − 19x by adding 19x to both sides of the equation. 11 − 15x = 13 − 19x 11 − 15x + 19x = 13 − 19x + 19x 4x + 11 = 13 Original equation. Add 19x to both sides. Simplify both sides. Next, eliminate 11 from the left-hand side of the last equation by subtracting 11 from both sides of the equation. 4x + 11 − 11 = 13 − 11 4x = 2 Subtract 11 both sides. Simplify both sides. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 68 Note how we have isolated all terms containing x on one side of the equation. Finally, to “undo” multiplying by 4, divide both sides of the equation by 4. 4x 2 = 4 4 1 x= 2 Divide both sides by 4. Reduce to lowest terms. 39. We need to isolate all terms containing x on one side of the equation. We can eliminate −19x from the right-hand side of 9x + 8 = 4 − 19x by adding 19x to both sides of the equation. 9x + 8 = 4 − 19x 9x + 8 + 19x = 4 − 19x + 19x 28x + 8 = 4 Original equation. Add 19x to both sides. Simplify both sides. Next, eliminate 8 from the left-hand side of the last equation by subtracting 8 from both sides of the equation. 28x + 8 − 8 = 4 − 8 28x = −4 Subtract 8 both sides. Simplify both sides. Note how we have isolated all terms containing x on one side of the equation. Finally, to “undo” multiplying by 28, divide both sides of the equation by 28. −4 28x = 28 28 1 x=− 7 Divide both sides by 28. Reduce to lowest terms. 41. We need to isolate all terms containing x on one side of the equation. We can eliminate −18x from the right-hand side of 7x + 11 = 16 − 18x by adding 18x to both sides of the equation. 7x + 11 = 16 − 18x 7x + 11 + 18x = 16 − 18x + 18x 25x + 11 = 16 Original equation. Add 18x to both sides. Simplify both sides. Next, eliminate 11 from the left-hand side of the last equation by subtracting 11 from both sides of the equation. 25x + 11 − 11 = 16 − 11 25x = 5 Second Edition: 2012-2013 Subtract 11 both sides. Simplify both sides. 2.2. SOLVING EQUATIONS: MULTIPLE STEPS 69 Note how we have isolated all terms containing x on one side of the equation. Finally, to “undo” multiplying by 25, divide both sides of the equation by 25. 25x 5 = 25 25 1 x= 5 Divide both sides by 25. Reduce to lowest terms. 43. We need to isolate all terms containing x on one side of the equation. We can eliminate 4x from the right-hand side of 12x + 9 = 4x + 7 by subtracting 4x from both sides of the equation. 12x + 9 = 4x + 7 12x + 9 − 4x = 4x + 7 − 4x 8x + 9 = 7 Original equation. Subtract 4x from both sides. Simplify both sides. Next, eliminate 9 from the left-hand side of the last equation by subtracting 9 from both sides of the equation. 8x + 9 − 9 = 7 − 9 8x = −2 Subtract 9 both sides. Simplify both sides. Note how we have isolated all terms containing x on one side of the equation. Finally, to “undo” multiplying by 8, divide both sides of the equation by 8. 8x −2 = 8 8 1 x=− 4 Divide both sides by 8. Reduce to lowest terms. 45. We’ll ﬁrst simplify the expression on the left-hand side of the equation using the Rules Guiding Order of Operations. 8(5x − 3) − 3(4x + 6) = 4 40x − 24 − 12x − 18 = 4 28x − 42 = 4 Original equation. Multiply: 8(5x − 3) = 40x − 24. Multiply: −3(4x + 6) = −12x − 18. Add: 40x − 12x = 28x. Add: −24 − 18 = −42. Next, isolate terms containing the variable x on one side of the equation. To remove the term −42 from the left-hand side, add 42 to both sides of the equation. 28x − 42 + 42 = 4 + 42 28x = 46 Add 42 to both sides. Simplify both sides. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 70 Finally, to “undo” multiplying 28, divide both sides of the equation by 28. 28x 46 = 28 28 23 x= 14 Divide both sides by 28. Reduce. 47. We’ll ﬁrst simplify the expression on the left-hand side of the equation using the Rules Guiding Order of Operations. 2x − 4(4 − 9x) = 4(7x + 8) 2x − 16 + 36x = 28x + 32 38x − 16 = 28x + 32 Original equation. Multiply: −4(4 − 9x) = −16 + 36x. Multiply: 4(7x + 8) = 28x + 8. Add: 2x + 36x = 38x. Now we will isolate all terms containing x on one side of the equation. To remove the term 28x from the right-hand side, subtract 28x from both sides of the equation. 38x − 16 − 28x = 28x + 32 − 28x 10x − 16 = 32 Subtract 28x from both sides. Simplify both sides. To remove the term −16 from the left-hand side, add 16 to both sides of the equation. 10x − 16 + 16 = 32 + 16 10x = 48 Add 16 to both sides. Simplify both sides. Finally, to “undo” multiplying by 10, divide both sides of the equation by 10. 10x 48 = 10 10 24 x= 5 Divide both sides by 10. Reduce. 49. We’ll ﬁrst simplify the expression on the left-hand side of the equation using the Rules Guiding Order of Operations. 2(6 − 2x) − (4x − 9) = 9 12 − 4x − 4x + 9 = 9 21 − 8x = 9 Second Edition: 2012-2013 Original equation. Multiply: 2(6 − 2x) = 12 − 4x. Distribute the minus sign: −(4x − 9) = −4x + 9. Add: 12 + 9 = 21. Add: −4x − 4x = −8x. 2.2. SOLVING EQUATIONS: MULTIPLE STEPS 71 Next, isolate all terms containing the variable x on one side of the equation. To remove the term 21 from the left-hand side, subtract 21 from both sides of the equation. 21 − 8x − 21 = 9 − 21 −8x = −12 Subtract 21 from both sides. Simplify both sides. To “undo” multiplying by −8, divide both sides of the equation by −8. −12 −8x = −8 −8 3 x= 2 Divide both sides by −8. Reduce. 51. We’ll ﬁrst simplify the expression on the left-hand side of the equation using the Rules Guiding Order of Operations. 3(5x − 6) − 7(7x + 9) = 3 15x − 18 − 49x − 63 = 3 −34x − 81 = 3 Original equation. Multiply: 3(5x − 6) = 15x − 18. Multiply: −7(7x + 9) = −49x − 63. Add: 15x − 49x = −34x. Add: −18 − 63 = −81. Next, isolate terms containing the variable x on one side of the equation. To remove the term −81 from the left-hand side, add 81 to both sides of the equation. −34x − 81 + 81 = 3 + 81 −34x = 84 Add 81 to both sides. Simplify both sides. Finally, to “undo” multiplying −34, divide both sides of the equation by −34. −34x 84 = −34 −34 42 x=− 17 Divide both sides by −34. Reduce. 53. We’ll ﬁrst simplify the expression on the left-hand side of the equation using the Rules Guiding Order of Operations. 2x − 2(4 − 9x) = 8(6x + 2) 2x − 8 + 18x = 48x + 16 20x − 8 = 48x + 16 Original equation. Multiply: −2(4 − 9x) = −8 + 18x. Multiply: 8(6x + 2) = 48x + 2. Add: 2x + 18x = 20x. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 72 Now we will isolate all terms containing x on one side of the equation. To remove the term 48x from the right-hand side, subtract 48x from both sides of the equation. 20x − 8 − 48x = 48x + 16 − 48x −28x − 8 = 16 Subtract 48x from both sides. Simplify both sides. To remove the term −8 from the left-hand side, add 8 to both sides of the equation. −28x − 8 + 8 = 16 + 8 −28x = 24 Add 8 to both sides. Simplify both sides. Finally, to “undo” multiplying by −28, divide both sides of the equation by −28. 24 −28x = −28 −28 6 x=− 7 Divide both sides by −28. Reduce. 55. We’ll ﬁrst simplify the expression on the left-hand side of the equation using the Rules Guiding Order of Operations. 2(7 − 9x) − (2x − 8) = 7 14 − 18x − 2x + 8 = 7 22 − 20x = 7 Original equation. Multiply: 2(7 − 9x) = 14 − 18x. Distribute the minus sign: −(2x − 8) = −2x + 8. Add: 14 + 8 = 22. Add: −18x − 2x = −20x. Next, isolate all terms containing the variable x on one side of the equation. To remove the term 22 from the left-hand side, subtract 22 from both sides of the equation. 22 − 20x − 22 = 7 − 22 −20x = −15 Subtract 22 from both sides. Simplify both sides. To “undo” multiplying by −20, divide both sides of the equation by −20. −20x −15 = −20 −20 3 x= 4 Second Edition: 2012-2013 Divide both sides by −20. Reduce. 2.3. SOLVING EQUATIONS: CLEARING FRATIONS AND DECIMALS73 2.3 Solving Equations: Clearing Frations and Decimals 1. Multiply 16 and 9 to get 144, 9 9 x = 16 · 16 x 2 2 144 = x 2 = 72x then divide 144 by 2 to get 72. Associative property of multiplication. Multiply: 16 · 9 = 144. Divide: 144/2 = 72. Alternate solution: Divide 2 into 16 to get 8, then multiply 8 by 9 to get 72. 16 9 9 x = 16 · x 2 2 = (8 · 9) x = 72x Associative property of multiplication. Divide: 16/2 = 8. Multiply: 8 · 9 = 72. Note that the second method is more eﬃcient, because it involves smaller numbers, making it easier to perform the steps mentally. That is, write 9 x = 72x, 16 2 without writing down any steps. 3. Multiply 14 and 3 to get 42, then divide 42 by 2 to get 21. 3 3 14 x = 14 · x Associative property of multiplication. 2 2 42 = x Multiply: 14 · 3 = 42. 2 = 21x Divide: 42/2 = 21. Alternate solution: Divide 2 into 14 to get 7, then multiply 7 by 3 to get 21. 14 3 3 x = 14 · x 2 2 = (7 · 3) x = 21x Associative property of multiplication. Divide: 14/2 = 7. Multiply: 7 · 3 = 21. Note that the second method is more eﬃcient, because it involves smaller numbers, making it easier to perform the steps mentally. That is, write 3 x = 21x, 14 2 without writing down any steps. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 74 5. Multiply 70 and 9 to get 630, then divide 630 by 7 to get 90. 9 9 70 x = 70 · x Associative property of multiplication. 7 7 630 x Multiply: 70 · 9 = 630. = 7 = 90x Divide: 630/7 = 90. Alternate solution: Divide 7 into 70 to get 10, then multiply 10 by 9 to get 90. 9 9 x = 70 · 70 x Associative property of multiplication. 7 7 = (10 · 9) x = 90x Divide: 70/7 = 10. Multiply: 10 · 9 = 90. Note that the second method is more eﬃcient, because it involves smaller numbers, making it easier to perform the steps mentally. That is, write 9 x = 90x, 70 7 without writing down any steps. 7. Clear fractions from the equation by multiplying both sides by the least common denominator. The least common denominator in this case is 21. 9 1 5 − x− = Original equation. 7 3 3 9 1 5 21 − x − = 21 Multiply both sides by 21. 7 3 3 1 5 9 21 − x − 21 = 21 Distribute the 21 on each side. 7 3 3 −27x − 7 = 35 Multiply. Note that the fractions are now cleared from the equation. Next, isolate all terms containing the variable x on one side of the equation. We can remove the term −7 from the left-hand side by adding 7 to both sides of the equation. −27x − 7 + 7 = 35 + 7 −27x = 42 Add 7 to both sides. Simplify both sides. Finally, to “undo” multiplying by −27, divide both sides of the equation by −27. 42 −27x = −27 −27 14 x=− 9 Second Edition: 2012-2013 Divide both sides by −27. Simplify both sides. 2.3. SOLVING EQUATIONS: CLEARING FRATIONS AND DECIMALS75 9. Clear fractions from the equation by multiplying both sides by the least common denominator. The least common denominator in this case is 9. 7 5 2 4 x+ = x− 9 3 3 3 7 5 2 4 9 x+ x− =9 3 9 3 3 4 5 2 7 x +9 x −9 − =9 9 3 9 3 3 21x + 5 = 6x − 12 Original equation. Multiply both sides by 9. Distribute the 9 on each side. Multiply. Note that the fractions are now cleared from the equation. Next, isolate all terms containing the variable x on one side of the equation. We can remove the term 6x from the right-hand side by subtracting 6x from both sides of the equation. 21x + 5 − 6x = 6x − 12 − 6x 15x + 5 = −12 Subtract 6x from both sides. Simplify both sides. Next, we can remove the term 5 from the left-hand side by subtracting 5 from both sides of the equation. 15x + 5 − 5 = −12 − 5 15x = −17 Subtract 5 from both sides. Simplify both sides. Finally, to “undo” multiplying by 15, divide both sides of the equation by 15. 15x −17 = 15 15 17 x=− 15 Divide both sides by 15. Simplify both sides. 11. Clear fractions from the equation by multiplying both sides by the least common denominator. The least common denominator in this case is 28. 9 8 3 x− = 4 7 2 9 8 3 x− 28 = 28 4 7 2 8 3 9 x − 28 = 28 28 4 7 2 63x − 32 = 42 Original equation. Multiply both sides by 28. Distribute the 28 on each side. Multiply. Note that the fractions are now cleared from the equation. Next, isolate all terms containing the variable x on one side of the equation. We can remove the Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 76 term −32 from the left-hand side by adding 32 to both sides of the equation. 63x − 32 + 32 = 42 + 32 63x = 74 Add 32 to both sides. Simplify both sides. Finally, to “undo” multiplying by 63, divide both sides of the equation by 63. 63x 74 = 63 63 74 x= 63 Divide both sides by 63. Simplify both sides. 13. Clear fractions from the equation by multiplying both sides by the least common denominator. The least common denominator in this case is 12. 3 8 − x=− 4 3 3 8 12 − x = 12 − 4 3 −9x = −32 Original equation. Multiply both sides by 12. Multiply. To “undo” multiplying by −9, divide both sides of the equation by −9. −32 −9x = −9 −9 32 x= 9 Divide both sides by −9. Simplify. 15. Clear fractions from the equation by multiplying both sides by the least common denominator. The least common denominator in this case is 20. 3 6 = 4 5 3 6 20 x + = 20 4 5 6 3 = 20 20x + 20 4 5 x+ 20x + 15 = 24 Original equation. Multiply both sides by 20. On the left, distribute the 20. Multiply. Next, isolate all terms containing x on one side of the equation. 20x + 15 − 15 = 24 − 15 20x = 9 Second Edition: 2012-2013 Subtract 15 from both sides. Simplify both sides. 2.3. SOLVING EQUATIONS: CLEARING FRATIONS AND DECIMALS77 Finally, to “undo” multiplying by 20, divide both sides of the equation by 20. 20x 9 = 20 20 9 x= 20 Divide both sides by 20. Simplify both sides. 17. Clear fractions from the equation by multiplying both sides by the least common denominator. The least common denominator in this case is 60. 4 3 8 1 Original equation. − x− =− x− 3 3 4 5 1 4 8 3 60 − x − = 60 − x − Multiply both sides by 60. 3 3 4 5 4 8 1 3 60 − x − 60 = 60 − x − 60 − Distribute the 60 on each side. 3 3 4 5 −20x − 80 = −45x − 96 Multiply. Note that the fractions are now cleared from the equation. Next, isolate all terms containing the variable x on one side of the equation. We can remove the term −45x from the right-hand side by adding 45x to both sides of the equation. −20x − 80 + 45x = −45x − 96 + 45x 25x − 80 = −96 Add 45x to both sides. Simplify both sides. Next, we can remove the term −80 from the left-hand side by adding 80 to both sides of the equation. 25x − 80 + 80 = −96 + 80 25x = −16 Add 80 to both sides. Simplify both sides. Finally, to “undo” multiplying by 25, divide both sides of the equation by 25. 25x −16 = 25 25 16 x=− 25 Divide both sides by 25. Simplify both sides. 19. At a minimum, we need to move each decimal point two places to the right in order to clear the decimals from the equation. Consequently, we multiply both sides of the equation by 100. 2.39x + 0.71 = −1.98x + 2.29 100(2.39x + 0.71) = 100(−1.98x + 2.29) 239x + 71 = −198x + 229 Original Equation. Multiply both sides by 100. Distribute the 100. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 78 Note that the decimals are now cleared from the equation. Next, isolate all terms containing the variable x on one side of the equation. Remove the term −198x from the right-hand side by adding 198x to both sides of the equation. 239x + 71 + 198x = −198x + 229 + 198x 437x + 71 = 229 Add 198x to both sides. Simplify both sides. Subtract 71 from to eliminate the term 71 from the left-hand side of the equation. 437x + 71 − 71 = 229 − 71 437x = 158 Subtract 71 from both sides. Simplify both sides. Finally, to “undo” multiplying by 437, divide both sides of the equation by 437. 437x 158 = 437 437 158 x= 437 Divide both sides by 437. Simplify. 21. At a minimum, we need to move each decimal point two places to the right in order to clear the decimals from the equation. Consequently, we multiply both sides of the equation by 100. 0.4x − 1.55 = 2.14 100(0.4x − 1.55) = 100(2.14) 40x − 155 = 214 Original Equation. Multiply both sides by 100. Distribute the 100. Note that the decimals are now cleared from the equation. We can continue by adding 155 to both sides of the equation. 40x − 155 + 155 = 214 + 155 40x = 369 369 40x = 40 40 369 x= 40 Add 155 to both sides. Simplify both sides. Divide both sides by 40. Simplify. 23. At a minimum, we need to move each decimal point two places to the right in order to clear the decimals from the equation. Consequently, we multiply both sides of the equation by 100. 2.6x − 2.54 = −2.14x 100(2.6x − 2.54) = 100(−2.14x) 260x − 254 = −214x Second Edition: 2012-2013 Original Equation. Multiply both sides by 100. Distribute the 100. 2.3. SOLVING EQUATIONS: CLEARING FRATIONS AND DECIMALS79 Note that the decimals are now cleared from the equation. Next, isolate all terms containing the variable x on one side of the equation. Remove the term −214x from the right-hand side of the equation by adding 214x to both sides of the equation. 260x − 254 + 214x = −214x + 214x 474x − 254 = 0 Add 214x to both sides. Simplify both sides. Add 254 to both sides to remove the term −254 from the left-hand side of the equation. 474x − 254 + 254 = 0 + 254 474x = 254 Add 254 to both sides. Simplify both sides. Finally, to “undo” multiplying by 474, divide both sides of the equation by 474. 474x 254 = 474 474 127 x= 237 Divide both sides by 474. Simplify. 25. At a minimum, we need to move each decimal point one place to the right in order to clear the decimals from the equation. Consequently, we multiply both sides of the equation by 10. 0.7x = −2.3x − 2.8 10(0.7x) = 10(−2.3x − 2.8) 7x = −23x − 28 Original Equation. Multiply both sides by 10. Distribute the 10. Note that the decimals are now cleared from the equation. Next, isolate all terms containing the variable x on one side of the equation. We can remove the term −23x from the right-hand side by adding 23x to both sides of the equation. 7x + 23x = −23x − 28 + 23x 30x = −28 Add 23x to both sides. Simplify both sides. To “undo” multiplying by 30, divide both sides of the equation by 30. 30x −28 = 30 30 14 x=− 15 Divide both sides by 30. Simplify. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 80 27. At a minimum, we need to move each decimal point one place to the right in order to clear the decimals from the equation. Consequently, we multiply both sides of the equation by 10. −4.8x − 2.7 = −1.9 10(−4.8x − 2.7) = 10(−1.9) −48x − 27 = −19 Original Equation. Multiply both sides by 10. Distribute the 10. Note that the decimals are now cleared from the equation. We can continue by adding 27 to both sides of the equation. −48x − 27 + 27 = −19 + 27 −48x = 8 −48x 8 = −48 −48 1 x=− 6 Add 27 to both sides. Simplify both sides. Divide both sides by −48. Simplify. 29. At a minimum, we need to move each decimal point one place to the right in order to clear the decimals from the equation. Consequently, we multiply both sides of the equation by 10. 1.7x + 2.1 = −1.6x + 2.5 10(1.7x + 2.1) = 10(−1.6x + 2.5) 17x + 21 = −16x + 25 Original Equation. Multiply both sides by 10. Distribute the 10. Note that the decimals are now cleared from the equation. Next, isolate all terms containing the variable x on one side of the equation. Remove −16x from the right-hand side by adding 16x to both sides of the equation. 17x + 21 + 16x = −16x + 25 + 16x 33x + 21 = 25 Add 16x to both sides. Simplify both sides. Subtract 21 from both sides to remove the term 21 from the left-hand side of the equation. 33x + 21 − 21 = 25 − 21 33x = 4 Subtract 21 from both sides. Simplify both sides. Finally, to “undo” multiplying by 33, divide both sides of the equation by 33. 33x 4 = 33 33 4 x= 33 Second Edition: 2012-2013 Divide both sides by 33. Simplify. 2.4. FORMULAE 81 31. At a minimum, we need to move each decimal point one place to the right in order to clear the decimals from the equation. Consequently, we multiply both sides of the equation by 10. 2.5x + 1.9 = 0.9x 10(2.5x + 1.9) = 10(0.9x) 25x + 19 = 9x Original Equation. Multiply both sides by 10. Distribute the 10. Note that the decimals are now cleared from the equation. Next, isolate all terms containing the variable x on one side of the equation. Remove the term 9x from the right-hand side by subtracting 9x from both sides of the equation. 25x + 19 − 9x = 9x − 9x 16x + 19 = 0 Subtract 9x from both sides. Simplify both sides. Subtract 19 from both sides to remove the term 19 from the left-hand side of the equation. 16x + 19 − 19 = 0 − 19 16x = −19 Subtract 19 from both sides. Simplify both sides. Finally, to “undo” multiplying by 16, divide both sides of the equation by 16. −19 16x = 16 16 19 x=− 16 2.4 Divide both sides by 16. Simplify. Formulae 1. We are instructed to solve the equation F = kx for x. Thus, we must isolate all terms containing the variable x on one side of the equation. We begin by dividing both sides of the equation by k. F = kx kx F = k k F =x k Original equation. Divide both sides by k. Simplify. Note that this last equation is identical to the following equation x= F k Note that we have x =“Stuﬀ”, where “Stuﬀ” contains no occurrences of x, the variable we are solving for. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 82 3. We are instructed to solve the equation E = mc2 for m. Thus, we must isolate all terms containing the variable m on one side of the equation. We begin by dividing both sides of the equation by c2 . E = mc2 E mc = 2 2 c c E =m c2 2 Original equation. Divide both sides by c2 . Simplify. Note that this last equation is identical to the following equation m= E c2 We now have m =“Stuﬀ”, where “Stuﬀ” contains no occurrences of m, the variable we are solving for. 5. We are instructed to solve the equation A = πr1 r2 for r2 . Thus, we must isolate all terms containing the variable r2 on one side of the equation. We begin by dividing both sides of the equation by πr1 . A = πr1 r2 A πr1 r2 = πr1 πr1 A = r2 πr1 Original equation. Divide both sides by πr1 . Simplify. Note that this last equation is identical to the following equation r2 = A πr1 Note that we have r2 =“Stuﬀ”, where “Stuﬀ” contains no occurrences of r2 , the variable we are solving for. 7. We are instructed to solve the equation F = ma for a. Thus, we must isolate all terms containing the variable a on one side of the equation. We begin by dividing both sides of the equation by m. F = ma ma F = m m F =a m Second Edition: 2012-2013 Original equation. Divide both sides by m. Simplify. 2.4. FORMULAE 83 Note that this last equation is identical to the following equation F m Note that we have a =“Stuﬀ”, where “Stuﬀ” contains no occurrences of a, the variable we are solving for. a= 9. We are instructed to solve the equation C = 2πr for r. Thus, we must isolate all terms containing the variable r on one side of the equation. We begin by dividing both sides of the equation by 2π. C = 2πr C 2πr = 2π 2π C =r 2π Original equation. Divide both sides by 2π. Simplify. Note that this last equation is identical to the following equation C 2π Note that we have r =“Stuﬀ”, where “Stuﬀ” contains no occurrences of r, the variable we are solving for. r= 11. We are instructed to solve the equation y = mx + b for x. Thus, we must isolate all terms containing the variable x on one side of the equation. First, subtract b from both sides of the equation. y = mx + b y − b = mx + b − b Original equation. Subtract b from both sides. y − b = mx Combine like terms. Note that all the terms comtaining x, the variable we are solving for, are already isolated on one side of the equation. We need only divide both sides of the equation by m to complete the solution. y−b mx = m m y−b =x m Divide both sides by m. Simplify. Note that this last equation is identical to the following equation y−b Simplify. m Note that we have x =“Stuﬀ”, where “Stuﬀ” contains no occurrences of x, the variable we are solving for. x= Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 84 13. We are instructed to solve the equation F = qvB for v. Thus, we must isolate all terms containing the variable v on one side of the equation. We begin by dividing both sides of the equation by qB. F = qvB F qvB = qB qB F =v qB Original equation. Divide both sides by qB. Simplify. Note that this last equation is identical to the following equation v= F qB Note that we have v =“Stuﬀ”, where “Stuﬀ” contains no occurrences of v, the variable we are solving for. 1 15. We are instructed to solve the equation V = πr2 h for h. Thus, we must 3 isolate all terms containing the variable h on one side of the equation. First, clear the fractions by multiplying both sides of the equation by the common denominator, 3. 1 2 πr h 3 1 2 πr h 3(V ) = 3 3 V = 3V = πr2 h Original equation. Multiply both sides by 3. Simplify. Cancel 3’s. Note that all the terms comtaining h, the variable we are solving for, are already isolated on one side of the equation. We need only divide both sides of the equation by πr2 to complete the solution. πr2 h 3V = πr2 πr2 3V =h πr2 Divide both sides by πr2 . Simplify. Note that this last equation is identical to the following equation h= 3V πr2 Note that we have h =“Stuﬀ”, where “Stuﬀ” contains no occurrences of h, the variable we are solving for. Second Edition: 2012-2013 2.4. FORMULAE 85 V for R. Thus, we must 17. We are instructed to solve the equation I = R isolate all terms containing the variable R on one side of the equation. First, clear the fractions by multiplying both sides of the equation by the common denominator, R. I= V R R(I) = R V R Original equation. Multiply both sides by R. RI = V Simplify. Cancel R’s. Note that all the terms comtaining R, the variable we are solving for, are already isolated on one side of the equation. We need only divide both sides of the equation by I to complete the solution. V RI = I I V R= I Divide both sides by I. Note that we have R =“Stuﬀ”, where “Stuﬀ” contains no occurrences of R, the variable we are solving for. kqQ 19. We are instructed to solve the equation F = 2 for q. Thus, we must r isolate all terms containing the variable q on one side of the equation. First, clear the fractions by multiplying both sides of the equation by the common denominator, r2 . F = kqQ r2 r2 (F ) = r2 r2 F = kqQ kqQ r2 Original equation. Multiply both sides by r2 . Simplify. Cancel r2 ’s. Note that all the terms comtaining q, the variable we are solving for, are already isolated on one side of the equation. We need only divide both sides of the equation by kQ to complete the solution. r2 F kqQ = kQ kQ 2 r F =q kQ Divide both sides by kQ. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 86 Note that this last equation is identical to the following equation q= r2 F kQ Note that we have q =“Stuﬀ”, where “Stuﬀ” contains no occurrences of q, the variable we are solving for. 21. We are instructed to solve the equation P = 2W + 2L for W . Thus, we must isolate all terms containing the variable W on one side of the equation. First, subtract 2L from both sides of the equation. P = 2W + 2L P − 2L = 2W + 2L − 2L Original equation. Subtract 2L from both sides. P − 2L = 2W Combine like terms. Note that all the terms comtaining W , the variable we are solving for, are already isolated on one side of the equation. We need only divide both sides of the equation by 2 to complete the solution. 2W P − 2L = 2 2 P − 2L =W 2 Divide both sides by 2. Simplify. Note that this last equation is identical to the following equation W = P − 2L 2 Note that we have W =“Stuﬀ”, where “Stuﬀ” contains no occurrences of W , the variable we are solving for. 1 23. We are instructed to solve the equation A = h(b1 + b2 ) for h. Thus, we 2 must isolate all terms containing the variable h on one side of the equation. First, clear the fractions by multiplying both sides of the equation by the common denominator, 2. 1 h(b1 + b2 ) 2 1 h(b1 + b2 ) 2(A) = 2 2 A= 2A = h(b1 + b2 ) Second Edition: 2012-2013 Original equation. Multiply both sides by 2. Simplify. Cancel 2’s. 2.4. FORMULAE 87 Note that all the terms comtaining h, the variable we are solving for, are already isolated on one side of the equation. We need only divide both sides of the equation by b1 + b2 to complete the solution. 2A h(b1 + b2 ) = b1 + b2 b1 + b2 2A =h b1 + b2 Divide both sides by b1 + b2 . Simplify. Note that this last equation is identical to the following equation h= 2A b1 + b2 Note that we have h =“Stuﬀ”, where “Stuﬀ” contains no occurrences of h, the variable we are solving for. 25. We are instructed to solve the equation y − y0 = m(x − x0 ) for m. Thus, we must isolate all terms containing the variable m on one side of the equation. We begin by dividing both sides of the equation by x − x0 . y − y0 = m(x − x0 ) y − y0 m(x − x0 ) = x − x0 x − x0 y − y0 =m x − x0 Original equation. Divide both sides by x − x0 . Simplify. Note that this last equation is identical to the following equation m= y − y0 x − x0 Note that we have m =“Stuﬀ”, where “Stuﬀ” contains no occurrences of m, the variable we are solving for. GM m for M . Thus, we must 27. We are instructed to solve the equation F = r2 isolate all terms containing the variable M on one side of the equation. First, clear the fractions by multiplying both sides of the equation by the common denominator, r2 . GM m r2 GM m r2 (F ) = r2 r2 F = r2 F = GM m Original equation. Multiply both sides by r2 . Simplify. Cancel r2 ’s. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 88 Note that all the terms comtaining M , the variable we are solving for, are already isolated on one side of the equation. We need only divide both sides of the equation by Gm to complete the solution. GM m r2 F = Gm Gm r2 F =M Gm Divide both sides by Gm. Simplify. Note that this last equation is identical to the following equation: M= r2 F Gm Note that we have M =“Stuﬀ”, where “Stuﬀ” contains no occurrences of M , the variable we are solving for. 29. We are instructed to solve the equation d = vt for v. Thus, we must isolate all terms containing the variable v on one side of the equation. We begin by dividing both sides of the equation by t. d = vt vt d = t t d =v t Original equation. Divide both sides by t. Simplify. Note that this last equation is identical to the following equation v= d t Note that we have v =“Stuﬀ”, where “Stuﬀ” contains no occurrences of v, the variable we are solving for. 31. Start with the area formula and divide both sides by W . A = LW LW A = W W A =L W Hence: L= Second Edition: 2012-2013 A W 2.4. FORMULAE 89 To determine the length, substitute 1073 for A and 29 for W and simplify. 1073 29 L = 37 L= Hence, the length is L = 37 meters. 33. Start with the area formula, then divide both sides by h. A = bh A bh = h h A =b h Hence: b= A h Next, substitute 2418 for A, 31 for h, and simplify. 2418 31 b = 78 b= Hence, b = 78 feet. 35. Start with the area formula, then clear the equation of fractions by multiplying both sides of the equation by 2. 1 bh 2 1 2[A] = bh 2 2 A= 2A = bh Divide both sides by h. 2A bh = h h 2A =b h Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 90 Hence: b= 2A h Next, substitute 1332 for A, 36 for h, and simplify. 2(1332) 36 2664 b= 36 b = 74 b= Hence, b = 74 inches. 37. We need to isolate terms containing W on one side of the equation. Start with the perimeter equation and subtract 2L from both sides. P = 2W + 2L P − 2L = 2W + 2L − 2L P − 2L = 2W Divide both sides by 2 and simplify. P − 2L 2W = 2 2 P − 2L =W 2 Hence: W = P − 2L 2 Substitute 256 for P , 73 for L, then simplify. 256 − 2(73) 2 110 W = 2 W = 55 W = Hence, the width is W = 55 meters. Second Edition: 2012-2013 2.5. APPLICATIONS 2.5 91 Applications 1. We follow the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. Let θ represent the measure of the ﬁrst angle. 2. Set up an equation. A sketch will help summarize the information given in the problem. First, we sketch two angles whose sum is 90 degrees. The second angle is 6 degrees larger than 2 times the ﬁrst angle, so the second angle has measure 2θ + 6. 2θ + 6 θ The angles are complementary, so their sum is 90 degrees. Thus the equation is: θ + (2θ + 6) = 90 3. Solve the equation. Simplify the left-hand side by combining like terms. θ + (2θ + 6) = 90 3θ + 6 = 90 Subtract 6 from both sides of the equation, then divide both sides of the resulting equation by 3. 3θ + 6 − 6 = 90 − 6 3θ = 84 3θ 84 = 3 3 θ = 28 4. Answer the question. To ﬁnd the second angle, substitute 28 for θ in 2θ + 6 to get: 2θ + 6 = 2(28) + 6 = 62 Hence, the two angles are 28 and 62 degrees. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 92 5. Look back. Let’s label the angles with their numerical values. 62◦ 28◦ Clearly, their sum is 90◦ , so we have the correct answer. 3. We follow the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. Let θ represent the measure of the ﬁrst angle. 2. Set up an equation. A sketch will help summarize the information given in the problem. First, we sketch two angles whose sum is 180 degrees. The second angle is 10 degrees larger than 4 times the ﬁrst angle, so the second angle has measure 4θ + 10. 4θ + 10 θ The angles are supplementary, so their sum is 180 degrees. Thus the equation is: θ + (4θ + 10) = 180 3. Solve the equation. Simplify the left-hand side by combining like terms. θ + (4θ + 10) = 180 5θ + 10 = 180 Second Edition: 2012-2013 2.5. APPLICATIONS 93 Subtract 10 from both sides of the equation, then divide both sides of the resulting equation by 5. 5θ + 10 − 10 = 180 − 10 5θ = 170 5θ 170 = 5 5 θ = 34 4. Answer the question. To ﬁnd the second angle, substitute 34 for θ in 4θ + 10 to get: 4θ + 10 = 4(34) + 10 = 146 Hence, the two angles are 34 and 146 degrees. 5. Look back. Let’s label the angles with their numerical values. 146◦ 34◦ Clearly, their sum is 180◦ , so we have the correct answer. 5. In the solution, we address each step of the Requirements for Word Problem Solutions. 1. Set up a Variable Dictionary. An example of three consecutive integers is 19, 20, and 21. These are not the integers we seek, but they do give us some sense of the meaning of three consecutive integers. Note that each consecutive integer is one larger than the preceding integer. Thus, if k is the length of the ﬁrst side of the triangle, then the next two sides are k + 1 and k + 2. In this example, our variable dictionary will take the form of a well-labeled ﬁgure. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 94 k+2 k k+1 2. Set up an Equation. The perimeter of the triangle is the sum of the three sides. If the perimeter is 483 meters, then: k + (k + 1) + (k + 2) = 483 3. Solve the Equation. To solve for k, ﬁrst simplify the left-hand side of the equation by combining like terms. k + (k + 1) + (k + 2) = 483 3k + 3 = 483 3k + 3 − 3 = 483 − 3 3k = 480 480 3k = 3 3 k = 160 Original equation. Combine like terms. Subtract 3 from both sides. Simplify. Divide both sides by 3. Simplify. 4. Answer the Question. Thus, the ﬁrst side has length 160 meters. Because the next two consecutive integers are k + 1 = 161 and k + 2 = 162, the three sides of the triangle measure 160, 161, and 162 meters, respectively. 5. Look Back. An image helps our understanding. The three sides are consecutive integers. 162 meters 160 meters 161 meters Note that the perimeter (sum of the three sides) is: 160 meters + 161 meters + 162 meters = 483 meters (2.1) Thus, the perimeter is 483 meters, as it should be. Our solution is correct. Second Edition: 2012-2013 2.5. APPLICATIONS 95 7. We follow the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. Let x represent the unknown number. 2. Set up an equation. The statement “four less than eight times a certain number is −660” becomes the equation: 8x − 4 = −660 3. Solve the equation. Add 4 to both sides, then divide the resulting equation by 8. 8x − 4 = −660 8x − 4 + 4 = −660 + 4 8x = −656 8x −656 = 8 8 x = −82 4. Answer the question. The unknown number is −82. 5. Look back. “Four less than eight times −82” translates as 8(−82) − 4, which equals −660. The solution make sense. 9. In the solution, we address each step of the Requirements for Word Problem Solutions. 1. Set up a Variable Dictionary. Let d represent the distance left for Alan to hike. Because Alan is four times further from the beginning of the trail than the end, the distance Alan has already completed is 4d. Let’s construct a little table to help summarize the information provided in this problem. Section of Trail Distance (mi) Distance to ﬁnish Distance from start d 4d Total distance 70 2. Set up an Equation. As you can see in the table above, the second column shows that the sum of the two distances is 70 miles. In symbols: d + 4d = 70 Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 96 3. Solve the Equation. To solve for d, ﬁrst simplify the left-hand side of the equation by combining like terms. d + 4d = 70 5d = 70 5d 70 = 5 5 d = 14 Original equation. Combine like terms. Divide both sides by 5. Simplify. 4. Answer the Question. Alan still has 14 miles to hike. 5. Look Back. Because the amount left to hike is d = 14 miles, Alan’s distance from the start of the trail is 4d = 4(14), or 56 miles. If we arrange these results in tabular form, it is evident that not only is the distance from the start of the trail four times that of the distance left to the ﬁnish, but also the sum of their lengths is equal to the total length of the trail. Section of Trail Distance (mi) Distance (mi) Distance to ﬁnish Distance from start d 4d 14 56 Total distance 70 70 Thus, we have the correct solution. 11. We follow the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. Let p represent the percentage of Martha ’s sixth grade class that is absent. 2. Set up the equation. The question is “what percent of the class size equals the number of students absent?” The phrase “p percent of 36 is 2” becomes the equation: p × 36 = 2 Or equivalently: 36p = 2 3. Solve the equation. Use a calculator to help divide both sides of the equation by 36. 36p = 2 2 36p = 36 36 p = 0.0555555556 Second Edition: 2012-2013 2.5. APPLICATIONS 97 4. Answer the question. We need to change our answer to a percent. First, round the percentage answer p to the nearest hundredth. Test digit 0.0 5 5 5555556 Rounding digit Because the test digit is greater than or equal to 5, add 1 to the rounding digit, then truncate. Hence, to the nearest hundredth, 0.0555555556 is approximately 0.06. To change this answer to a percent, multiply by 100, or equivalently, move the decimal two places to the right. Hence, 6% of Martha’s sixth grade class is absent. 5. Look back. If we take 6% of Martha’s class size, we get: 6% × 36 = 0.06 × 36 = 2.16 Rounded to the nearest student, this means there are 2 students absent, indicating we’ve done the problem correctly. 13. We follow the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. Let x represent the length of the ﬁrst piece. 2. Set up an equation. The second piece is 3 times as long as the ﬁrst piece, so the second piece has length 3x. The third piece is 6 centimeters longer than the ﬁrst piece, so the second piece has length x + 6. Let’s construct a table to summarize the information provided in this problem. Piece Length (centimeters) First Second Third Total length x 3x x+6 211 As you can see in the table above, the second column shows that the sum of the three pieces is 211 centimeters. Hence, the equation is: x + 3x + (x + 6) = 211 Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 98 3. Solve the equation. First, simplify the left-hand side of the equation by combining like terms. x + 3x + (x + 6) = 211 5x + 6 = 211 Subtract 6 from both sides of the equation, then divide both sides of the resulting equation by 5. 5x + 6 − 6 = 211 − 6 5x = 205 5x 205 = 5 5 x = 41 4. Answer the question. Let’s add a column to our table to list the length of the three pieces. The lengths of the second and third pieces are found by substituting 41 for x in 3x and x + 6. Piece First Second Third Total length Length (centimeters) Length (centimeters) x 3x x+6 41 123 47 211 211 5. Look back. The third column of the table above shows that the lengths sum to 211 centimeters, so we have the correct solution. 15. In the solution, we address each step of the Requirements for Word Problem Solutions. 1. Set up a Variable Dictionary. An example of three consecutive even integers is 18, 20, and 22. These are not the integers we seek, but they do give us some sense of the meaning of three consecutive even integers. Note that each consecutive even integer is two larger than the preceding integer. Thus, if k is the length of the ﬁrst side of the triangle, then the next two sides are k+2 and k+4. In this example, our variable dictionary will take the form of a well-labeled ﬁgure. Second Edition: 2012-2013 2.5. APPLICATIONS 99 k+4 k k+2 2. Set up an Equation. The perimeter of the triangle is the sum of the three sides. If the perimeter is 450 yards, then: k + (k + 2) + (k + 4) = 450 3. Solve the Equation. To solve for k, ﬁrst simplify the left-hand side of the equation by combining like terms. k + (k + 2) + (k + 4) = 450 3k + 6 = 450 3k + 6 − 6 = 450 − 6 3k = 444 444 3k = 3 3 k = 148 Original equation. Combine like terms. Subtract 6 from both sides. Simplify. Divide both sides by 3. Simplify. 4. Answer the Question. Thus, the ﬁrst side has length 148 yards. Because the next two consecutive even integers are k+2 = 150 and k+4 = 152, the three sides of the triangle measure 148, 150, and 152 yards, respectively. 5. Look Back. An image helps our understanding. The three sides are consecutive even integers. 152 yards 148 yards 150 yards Note that the perimeter (sum of the three sides) is: 148 yards + 150 yards + 152 yards = 450 yards (2.2) Thus, the perimeter is 450 yards, as it should be. Our solution is correct. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 100 17. We follow the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. Let x represent the length of the ﬁrst side of the triangle. 2. Set up an equation. The second side is 7 times as long as the ﬁrst side, so the second side has length 7x. The third side is 9 yards longer than the ﬁrst side, so the second side has length x + 9. Let’s sketch a diagram to summarize the information provided in this problem (the sketch is not drawn to scale). x+9 x 7x The sum of the three sides of the triangle equals the perimeter. Hence, the equation is: x + 7x + (x + 9) = 414 3. Solve the equation. First, simplify the left-hand side of the equation by combining like terms. x + 7x + (x + 9) = 414 9x + 9 = 414 Subtract 9 from both sides of the equation, then divide both sides of the resulting equation by 9. 9x + 9 − 9 = 414 − 9 9x = 405 9x 405 = 9 9 x = 45 4. Answer the question. Because the ﬁrst side is x = 45 yards, the second side is 7x = 315 yards, and the third side is x + 9 = 54 yards. 5. Look back. Let’s add the lengths of the three sides to our sketch. 54 yards 315 yards Second Edition: 2012-2013 45 yards 2.5. APPLICATIONS 101 Our sketch clearly indicates that the perimeter of the triangle is Perimeter = 45 + 315 + 54, or 414 yards. Hence, our solution is correct. 19. We follow the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. Let k represent the smallest of three consecutive odd integers. 2. Set up an equation. Because k is the smallest of three consecutive odd integers, the next two consecutive odd integers are k + 2 and k + 4. Therefore, the statement “the sum of three consecutive odd integers is −543” becomes the equation: k + (k + 2) + (k + 4) = −543 3. Solve the equation. First, combine like terms on the left-hand side of the equaton. k + (k + 2) + (k + 4) = −543 3k + 6 = −543 Subtract 6 from both sides, then divide both sides of the resulting equation by 3. 3k + 6 − 6 = −543 − 6 3k = −549 3k −549 = 3 3 k = −183 4. Answer the question. The smallest of three consecutive odd integers is −183. 5. Look back. Because the smallest of three consecutive odd integers is −183, the next two consecutive odd integers are −181, and −179. If we sum these integers, we get −183 + (−181) + (−179) = −543, so our solution is correct. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 102 21. We follow the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. Let θ represent the measure of angle A. 2. Set up an equation. A sketch will help summarize the information given in the problem. Because angle B is 4 times the size of angle A, the degree measure of angle B is represented by 4θ. Because angle C is 30 degrees larger than the degree measure of angle A, the degree measure of angle C is represented by θ + 30. C θ + 30 θ 4θ A B Because the sum of the three angles is 180◦, we have the following equation: θ + 4θ + (θ + 30) = 180 3. Solve the equation. Start by combining like terms on the left-hand side of the equation. θ + 4θ + (θ + 30) = 180 6θ + 30 = 180 Subtract 30 from both sides of the equation and simplify. 6θ + 30 − 30 = 180 − 30 6θ = 150 Divide both sides by 6. 150 6θ = 6 6 θ = 25 4. Answer the question. The degree measure of angle A is θ = 25◦ . The degree measure of angle B is 4θ = 100◦. The degree measure of angle C is θ + 30 = 55◦ . 5. Look back. Our ﬁgure now looks like the following. Second Edition: 2012-2013 2.5. APPLICATIONS 103 C 55◦ 25◦ 100◦ A B Note that 25 + 100 + 55 = 180, so our solution is correct. 23. We follow the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. Let k represent the smallest of three consecutive integers. 2. Set up an equation. Because k is the smallest of three consecutive integers, the next two consecutive integers are k + 1 and k + 2. Therefore, the statement “the sum of three consecutive integers is −384” becomes the equation: k + (k + 1) + (k + 2) = −384 3. Solve the equation. First, combine like terms on the left-hand side of the equaton. k + (k + 1) + (k + 2) = −384 3k + 3 = −384 Subtract 3 from both sides, then divide both sides of the resulting equation by 3. 3k + 3 − 3 = −384 − 3 3k = −387 −387 3k = 3 3 k = −129 4. Answer the question. The smallest of three consecutive integers is k = −129, so the next two consecutive integers are −128 and −127. Therefore, the largest of the three consecutive integers is −127. 5. Look back. If we sum the integers −129, −128, and −127, we get −129 + (−128) + (−127) = −384, so our solution is correct. Second Edition: 2012-2013 104 CHAPTER 2. SOLVING LINEAR EQUATIONS 25. We follow the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. Let x represent the unknown number. 2. Set up an equation. The statement “seven more than two times a certain number is 181” becomes the equation: 7 + 2x = 181 3. Solve the equation. Subtract 7 from both sides, then divide the resulting equation by 2. 7 + 2x = 181 7 + 2x − 7 = 181 − 7 2x = 174 2x 174 = 2 2 x = 87 4. Answer the question. The unknown number is 87. 5. Look back. “Seven more than two times 87” translates as 7 + 2(87), which equals 181. The solution make sense. 27. In the solution, we address each step of the Requirements for Word Problem Solutions. 1. Set up a Variable Dictionary. An example of three consecutive odd integers is 19, 21, and 23. These are not the integers we seek, but they do give us some sense of the meaning of three consecutive odd integers. Note that each consecutive odd integer is two larger than the preceding integer. Thus, if k is the length of the ﬁrst side of the triangle, then the next two sides are k+2 and k+4. In this example, our variable dictionary will take the form of a well-labeled ﬁgure. k+4 k k+2 Second Edition: 2012-2013 2.5. APPLICATIONS 105 2. Set up an Equation. The perimeter of the triangle is the sum of the three sides. If the perimeter is 537 feet, then: k + (k + 2) + (k + 4) = 537 3. Solve the Equation. To solve for k, ﬁrst simplify the left-hand side of the equation by combining like terms. k + (k + 2) + (k + 4) = 537 3k + 6 = 537 3k + 6 − 6 = 537 − 6 3k = 531 3k 531 = 3 3 k = 177 Original equation. Combine like terms. Subtract 6 from both sides. Simplify. Divide both sides by 3. Simplify. 4. Answer the Question. Thus, the ﬁrst side has length 177 feet. Because the next two consecutive odd integers are k+2 = 179 and k+4 = 181, the three sides of the triangle measure 177, 179, and 181 feet, respectively. 5. Look Back. An image helps our understanding. The three sides are consecutive odd integers. 181 feet 177 feet 179 feet Note that the perimeter (sum of the three sides) is: 177 feet + 179 feet + 181 feet = 537 feet (2.3) Thus, the perimeter is 537 feet, as it should be. Our solution is correct. 29. We follow the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. Let M represent the marked price of the article. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 106 2. Solve the equation. Because the store oﬀers a 14% discount, Yao pays 86% for the article. Thus, the question becomes “86% of the marked price is $670.8.” This translates into the equation 86% × M = 670.8, or equivalently, 0.86M = 670.8 Use a calculator to help divide both sides by 0.86. 0.86M 670.8 = 0.86 0.86 M = 780 3. Answer the question. Hence, the original marked price was $780. 4. Look back. Because the store oﬀers a 14% discount, Yao has to pay 86% for the article. Check what 86% of the marked price will be. 86% × 780 = 0.86 × 780 = 670.8 That’s the sales price that Yao paid. Hence, we’ve got the correct solution. 31. We follow the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. Let k represent the smallest of three consecutive even integers. 2. Set up an equation. Because k is the smallest of three consecutive even integers, the next two consecutive even integers are k + 2 and k + 4. Therefore, the statement “the sum of three consecutive even integers is −486” becomes the equation: k + (k + 2) + (k + 4) = −486 3. Solve the equation. First, combine like terms on the left-hand side of the equaton. k + (k + 2) + (k + 4) = −486 3k + 6 = −486 Second Edition: 2012-2013 2.5. APPLICATIONS 107 Subtract 6 from both sides, then divide both sides of the resulting equation by 3. 3k + 6 − 6 = −486 − 6 3k = −492 3k −492 = 3 3 k = −164 4. Answer the question. The smallest of three consecutive even integers is −164. 5. Look back. Because the smallest of three consecutive even integers is −164, the next two consecutive even integers are −162, and −160. If we sum these integers, we get −164 + (−162) + (−160) = −486, so our solution is correct. 33. We follow the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. Let M represent the amount invested in the mutal fund. 2. Set up the equation. We’ll use a table to help summarize the information in this problem. Because the amount invested in the certiﬁcate of deposit is $3,500 more than 6 times the amount invested in the mutual fund, we represent the amount invested in the certiﬁcate of deposit with the expression 6M + 3500. Investment Mutual fund Certiﬁcate of deposit Totals Amount invested M 6M + 3500 45500 The second column of the table gives us the needed equation. The two investment amounts must total $45,500. M + (6M + 3500) = 45500 Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 108 3. Solve the equation. To solve the equation, ﬁrst combine like terms on the left-hand side of the equation. M + (6M + 3500) = 45500 7M + 3500 = 45500 Subtract 3500 from both sides of the equation and simplify. 7M + 3500 − 3500 = 45500 − 3500 7M = 42000 Divide both sides of the equation by 7. 7M 42000 = 7 7 M = 6000 4. Answer the question. The amount invested in the mutual fund is M = $6, 000. The amount invested in the certiﬁcate of deposit is: Certiﬁcate of deposit = 6M + 3500 = 6(6000) + 3500 = 36000 + 3500 = 39500 Hence, the amount invested in the certiﬁcate of deposit is $39,500. 5. Look back. Note that the two amounts total 6000 + 39500 = 45500, so we have the correct solution. 2.6 Inequalities 1. Draw a number line, indicating the scale below the line. For each value 4, 3, −4, 7/8, and −8/3, plot the corresponding point on the line and label it with its value. −4 −5 −4 − 83 −3 7 8 −2 −1 0 1 2 3 4 3 4 5 The position of the numbers on the number line give us the ordering from smallest to largest: −4, −8/3, 7/8, 3, and 4. Second Edition: 2012-2013 2.6. INEQUALITIES 109 3. Draw a number line, indicating the scale below the line. For each value −5, 5, 4, 2/3, and 8/3, plot the corresponding point on the line and label it with its value. 2 3 −5 −5 −4 −3 −2 −1 0 8 3 1 2 3 4 5 4 5 The position of the numbers on the number line give us the ordering from smallest to largest: −5, 2/3, 8/3, 4, and 5. 5. {x : x ≥ −7} is read “the set of all x such that x is greater than or equal to −7”; that is, the set of all x that lie to the “right of” −7 or including −7 on the number line. Note that this does include the number −7. −7 7. {x : x < 2} is read “the set of all x such that x is less than 2”; that is, the set of all x that lie to the “left of” 2 on the number line. Note that this does not include the number 2. 2 9. (−∞, 2) = {x : x < 2}, and so it is read “the set of all x such that x is less than 2”; that is, the set of all x that lie to the “left of” 2 on the number line. Note that this does not include the number 2. 2 11. (6, ∞) = {x : x > 6}, and so it is read “the set of all x such that x is greater than 6”; that is, the set of all x that lie to the “right of” 6 on the number line. Note that this does not include the number 6. 6 Second Edition: 2012-2013 110 CHAPTER 2. SOLVING LINEAR EQUATIONS 13. {x : x < 7} is read “the set of all x such that x is greater than 7”; that is, the set of all x that lie to the “right of” 7 on the number line. Note that this does not include the number 7. 7 15. [0, ∞) = {x : x ≥ 0}, and so it is read “the set of all x such that x is greater than or equal to 0”; that is, the set of all x that lie to the “right of” 0 or including 0 on the number line. Note that this does include the number 0. 0 17. {x : x ≤ −2} is read “the set of all x such that x is less than or equal to −2”; that is, the set of all x that lie to the “left of” −2 or including −2 on the number line. Note that this does include the number −2. −2 19. (−∞, 3] = {x : x ≤ 3}, and so it is read “the set of all x such that x is less than or equal to 3”; that is, the set of all x that lie to the “left of” 3 or including 3 on the number line. Note that this does include the number 3. 3 21. Consider the shaded region on the given number line. 9 Note that every number to the left of 9, including 9, (i.e., “less than or equal to 9”) is shaded. Using set-builder notation, the shaded region is described by {x : x ≤ 9}. 23. Consider the shaded region on the given number line. Second Edition: 2012-2013 2.6. INEQUALITIES 111 −8 Note that every number to the left of −8 (i.e., “less than −8”) is shaded. Using set-builder notation, the shaded region is described by {x : x < −8}. 25. Consider the shaded region on the given number line. −2 Note that every number to the right of −2 (i.e., “greater than −2”) is shaded. Using set-builder notation, the shaded region is described by {x : x > −2}. 27. Consider the shaded region on the given number line. −3 Note that every number to the right of −3, including −3, (i.e., “greater than or equal to −3”) is shaded. Using set-builder notation, the shaded region is described by {x : x ≥ −3}. 29. Consider the shaded region on the given number line. 4 Note that every number to the right of 4 (i.e., “greater than 4”) is shaded. Using set-builder notation, the shaded region is described by (4, ∞). 31. Consider the shaded region on the given number line. −2 Note that every number to the left of −2 (i.e., “less than −2”) is shaded. Using interval notation, the shaded region is described by (−∞, −2). Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 112 33. Consider the shaded region on the given number line. 5 Note that every number to the left of 5, including 5, (i.e., “less than or equal to 5”) is shaded. Using interval notation, the shaded region is described by (−∞, 5]. 35. Consider the shaded region on the given number line. 1 Note that every number to the right of 1, including 1, (i.e., “greater than or equal to 1”) is shaded. Using interval notation, the shaded region is described by [1, ∞). 37. To “undo” adding 10, we subtract 10 from both sides of the inequality. x + 10 < 19 x + 10 − 10 < 19 − 10 Original inquality. Subtract 10 from both sides. x<9 Simplify both sides. Shade all real numbers that are “less than” or “left of” 9 on a number line. 9 Thus, using set-builder and interval notation, the solution is: {x : x < 9} = (−∞, 9) 39. To “undo” multiplying by 4, we divide both sides of the inequality by 4. Because we are dividing by a positive number, we do not reverse the inequality sign. 4x < 8 8 4x < 4 4 x<2 Original inquality. Divide both sides by 4. Simplify both sides. Shade all real numbers that are “less than” or “left of” 2 on a number line. Second Edition: 2012-2013 2.6. INEQUALITIES 113 2 Thus, using set-builder and interval notation, the solution is: {x : x < 2} = (−∞, 2) 41. To “undo” multiplying by −2, we divide both sides of the inequality by −2. Because we are dividing by a negative number, we reverse the inequality sign. −2x ≤ −2 −2x −2 ≥ −2 −2 Original inquality. Divide both sides by −2 and reverse the inequality sign. Simplify both sides. x≥1 Shade all real numbers that are “greater than or equal to” or “right of or including” 1 on a number line. 1 Thus, using set-builder and interval notation, the solution is: {x : x ≥ 1} = [1, ∞) 43. To “undo” subtracting 18, we add 18 to both sides of the inequality. x − 18 > −10 x − 18 + 18 > −10 + 18 Original inquality. Add 18 to both sides. x>8 Simplify both sides. Shade all real numbers that are “greater than” or “right of” 8 on a number line. 8 Thus, using set-builder and interval notation, the solution is: {x : x > 8} = (8, ∞) Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 114 45. We need to isolate terms containing x on one side of the inequality. We begin by adding 9x to both sides of the inequality. −5x − 6 ≥ 4 − 9x −5x − 6 + 9x ≥ 4 − 9x + 9x Original inquality. Add 9x to both sides. 4x − 6 ≥ 4 Simplify both sides. We continue to isolate terms containing x on one side of the inequality. We next add 6 to both sides of the inequality. 4x − 6 + 6 ≥ 4 + 6 Add 6 to both sides. 4x ≥ 10 Simplify both sides. To “undo” multiplying by 4, divide both sides by 4. Since we are dividing both sides by a positive number, we do not reverse the inequality sign. 4x 10 ≥ 4 4 5 x≥ 2 Divide both sides by 4. Reduce to lowest terms. Shade all real numbers that are “greater than or equal to” or “right of or including” 5/2 on a number line. 5/2 Thus, using set-builder and interval notation, the solution is: {x : x ≥ 5/2} = [5/2, ∞) 47. To “undo” subtracting 6, add 6 to both sides of the inequality. 16x − 6 ≤ 18 16x − 6 + 6 ≤ 18 + 6 16x ≤ 24 Original inquality. Add 6 to both sides. Simplify both sides. To “undo” multiplying by 16, divide both sides by 16. Since we are dividing both sides by a positive number, we do not reverse the inequality sign. 16x 24 ≤ 16 16 3 x≤ 2 Divide both sides by 16. Reduce to lowest terms. Shade all real numbers that are “less than or equal to” or “left of or including” 3/2 on a number line. Second Edition: 2012-2013 2.6. INEQUALITIES 115 3/2 Thus, using set-builder and interval notation, the solution is: {x : x ≤ 3/2} = (−∞, 3/2] 49. We need to isolate terms containing x on one side of the inequality. We begin by adding 4x to both sides of the inequality. −14x − 6 ≥ −10 − 4x −14x − 6 + 4x ≥ −10 − 4x + 4x Original inquality. Add 4x to both sides. −10x − 6 ≥ −10 Simplify both sides. We continue to isolate terms containing x on one side of the inequality. We next add 6 to both sides of the inequality. −10x − 6 + 6 ≥ −10 + 6 −10x ≥ −4 Add 6 to both sides. Simplify both sides. To “undo” multiplying by −10, divide both sides by −10. Since we are dividing both sides by a negative number, we reverse the inequality sign. −10x −4 ≤ −10 −10 x≤ Divide both sides by −10 and reverse the inequality sign. 2 5 Reduce to lowest terms. Shade all real numbers that are “less than or equal to” or “left of or including” 2/5 on a number line. 2/5 Thus, using set-builder and interval notation, the solution is: {x : x ≤ 2/5} = (−∞, 2/5] 51. To “undo” adding 18, subtract 18 from both sides of the inequality. 5x + 18 < 38 5x + 18 − 18 < 38 − 18 5x < 20 Original inquality. Subtract 18 from both sides. Simplify both sides. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 116 To “undo” multiplying by 5, divide both sides by 5. Since we are dividing both sides by a positive number, we do not reverse the inequality sign. 5x 20 < 5 5 x<4 Divide both sides by 5. Simplify both sides. Shade all real numbers that are “less than” or “left of” 4 on a number line. 4 Thus, using set-builder and interval notation, the solution is: {x : x < 4} = (−∞, 4) 53. We need to isolate terms containing x on one side of the inequality. We begin by adding 6x to both sides of the inequality. −16x − 5 ≥ −11 − 6x −16x − 5 + 6x ≥ −11 − 6x + 6x Original inquality. Add 6x to both sides. −10x − 5 ≥ −11 Simplify both sides. We continue to isolate terms containing x on one side of the inequality. We next add 5 to both sides of the inequality. −10x − 5 + 5 ≥ −11 + 5 Add 5 to both sides. −10x ≥ −6 Simplify both sides. To “undo” multiplying by −10, divide both sides by −10. Since we are dividing both sides by a negative number, we reverse the inequality sign. −10x −6 ≤ −10 −10 x≤ Divide both sides by −10 and reverse the inequality sign. 3 5 Reduce to lowest terms. Shade all real numbers that are “less than or equal to” or “left of or including” 3/5 on a number line. 3/5 Thus, using set-builder and interval notation, the solution is: {x : x ≤ 3/5} = (−∞, 3/5] Second Edition: 2012-2013 2.6. INEQUALITIES 117 55. We need to isolate terms containing x on one side of the inequality. We begin by adding 8x to both sides of the inequality. 2x − 9 ≥ 5 − 8x Original inquality. 2x − 9 + 8x ≥ 5 − 8x + 8x 10x − 9 ≥ 5 Add 8x to both sides. Simplify both sides. We continue to isolate terms containing x on one side of the inequality. We next add 9 to both sides of the inequality. 10x − 9 + 9 ≥ 5 + 9 Add 9 to both sides. 10x ≥ 14 Simplify both sides. To “undo” multiplying by 10, divide both sides by 10. Since we are dividing both sides by a positive number, we do not reverse the inequality sign. 10x 14 ≥ 10 10 7 x≥ 5 Divide both sides by 10. Reduce to lowest terms. Shade all real numbers that are “greater than or equal to” or “right of or including” 7/5 on a number line. 7/5 Thus, using set-builder and interval notation, the solution is: {x : x ≥ 7/5} = [7/5, ∞) 57. To “undo” subtracting 4, add 4 to both sides of the inequality. −10x − 4 ≤ 18 −10x − 4 + 4 ≤ 18 + 4 −10x ≤ 22 Original inquality. Add 4 to both sides. Simplify both sides. To “undo” multiplying by −10, divide both sides by −10. Since we are dividing both sides by a negative number, we reverse the inequality sign. −10x 22 ≥ −10 −10 x≥− 11 5 Divide both sides by −10 and reverse the inequality sign. Reduce to lowest terms. Shade all real numbers that are “greater than or equal to” or “right of or including” −11/5 on a number line. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 118 −11/5 Thus, using set-builder and interval notation, the solution is: {x : x ≥ −11/5} = [−11/5, ∞) 59. To “undo” adding 4, subtract 4 from both sides of the inequality. −12x + 4 < −56 Original inquality. −12x + 4 − 4 < −56 − 4 −12x < −60 Subtract 4 from both sides. Simplify both sides. To “undo” multiplying by −12, divide both sides by −12. Since we are dividing both sides by a negative number, we reverse the inequality sign. −60 −12x > −12 −12 Divide both sides by −12 and reverse the inequality sign. Simplify both sides. x>5 Shade all real numbers that are “greater than” or “right of” 5 on a number line. 5 Thus, using set-builder and interval notation, the solution is: {x : x > 5} = (5, ∞) 61. We need to isolate terms containing x on one side of the inequality. We begin by subtracting 6x from both sides of the inequality. 15x + 5 < 6x + 2 15x + 5 − 6x < 6x + 2 − 6x 9x + 5 < 2 Original inquality. Subtract 6x from both sides. Simplify both sides. We continue to isolate terms containing x on one side of the inequality. We next subtract 5 from both sides of the inequality. 9x + 5 − 5 < 2 − 5 9x < −3 Second Edition: 2012-2013 Subtract 5 from both sides. Simplify both sides. 2.6. INEQUALITIES 119 To “undo” multiplying by 9, divide both sides by 9. Since we are dividing both sides by a positive number, we do not reverse the inequality sign. −3 9x < 9 9 1 x<− 3 Divide both sides by 9. Reduce to lowest terms. Shade all real numbers that are “less than” or “left of” −1/3 on a number line. −1/3 Thus, using set-builder and interval notation, the solution is: {x : x < −1/3} = (−∞, −1/3) 63. The common denominator is 8. Clear the fractions from the inequality by multiplying both sides of the inequality by 8. 9 3 x> 2 8 3 9 8 x > 8 2 8 Original inequality. Multiply both sides by 8. 12x > 9 Cancel and multiply. To “undo” multiplying by 12, divide both sides of the inequality by 12. Because we are dividing by a positive number, we do not reverse the inequality. 9 12x > 12 12 3 x> 4 Divide both sides by 12. Simplify. Shade all real numbers that are “greater than” or “right of” 3/4 on a number line. 3/4 Thus, using set-builder and interval notation, the solution is: {x : x > 3/4} = (3/4, ∞) Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 120 65. The common denominator is 10. We will now clear the fractions from the inequality by multiplying both sides of the inequality by 10. 3 9 < 2 5 3 9 10 x + < 10 2 5 3 9 10x + 10 < 10 2 5 x+ 10x + 15 < 18 Original inequality. Multiply both sides by 10. On the left, distribute the 10. Multiply. To “undo” the eﬀect of adding 15, subtract 15 from both sides of the inequality. 10x + 15 − 15 < 18 − 15 10x < 3 Subtract 15 from both sides. Simplify both sides. To “undo” the eﬀect of multiplying by 10, divide both sides of the inequality by 10. 3 10x < Divide both sides by 10. 10 10 3 x< Simplify both sides. 10 Shade all real numbers that are “less than” or “left of” 3/10 on a number line. 3/10 Thus, using set-builder and interval notation, the solution is: {x : x < 3/10} = (−∞, 3/10) 67. Thus, using set-builder and interval notation, the solution is: {x : x ≥ 5/7} = [5/7, ∞) 69. The common denominator is 56. We will now clear the fractions from the inequality by multiplying both sides of the inequality by 56. x− 3 9 ≥− 8 7 3 9 56 x − ≥ 56 − 8 7 3 9 ≥ 56 − 56x − 56 8 7 56x − 21 ≥ −72 Second Edition: 2012-2013 Original inequality. Multiply both sides by 56. On the left, distribute the 56. Multiply. 2.6. INEQUALITIES 121 To “undo” the eﬀect of subtracting 21, add 21 to both sides of the inequality. 56x − 21 + 21 ≥ −72 + 21 56x ≥ −51 Add 21 to both sides. Simplify both sides. To “undo” the eﬀect of multiplying by 56, divide both sides of the inequality by 56. 56x −51 ≥ Divide both sides by 56. 56 56 51 x≥− Simplify both sides. 56 Shade all real numbers that are “greater than or equal to” or “right of or including” −51/56 on a number line. −51/56 Thus, using set-builder and interval notation, the solution is: {x : x ≥ −51/56} = [−51/56, ∞) 71. The common denominator is 35. Clear the fractions from the inequality by multiplying both sides of the inequality by 35. 6 4 − x≤− 5 7 6 4 35 − x ≤ − 35 5 7 Original inequality. Multiply both sides by 35. −42x ≤ −20 Cancel and multiply. To “undo” multiplying by −42, divide both sides of the inequality by −42. Because we are dividing by a negative number, we reverse the inequality. −20 −42x ≥ Divide both sides by −42. −42 −42 10 x≥ Simplify. 21 Shade all real numbers that are “greater than or equal to” or “right of or including” 10/21 on a number line. 10/21 Thus, using set-builder and interval notation, the solution is: {x : x ≥ 10/21} = [10/21, ∞) Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 122 73. The common denominator is 45. Clear the fractions from the inequality by multiplying both sides of the inequality by 45. 6 7 5 2 − x− ≤ − 5 3 9 9 6 7 5 2 45 − x − − ≤ 45 5 3 9 9 −54x − 105 ≤ 25 − 10x Original inequality. Multiply both sides by 45. Cancel and multiply. We need to isolate all terms containing x on one side of the equation. To “undo” subtracting 10x, add 10x from both sides of the inequality. −54x − 105 + 10x ≤ 25 − 10x + 10x −44x − 105 ≤ 25 Add 10x to both sides. Simplify both sides. We continue to isolate terms containing x on one side of the inequality. To “undo” subtracting 105, add 105 from both sides of the inequality. −44x − 105 + 105 ≤ 25 + 105 Add 105 to both sides. −44x ≤ 130 Simplify both sides. To “undo” the eﬀect of multiplying by −44, divide both sides of the inequality by −44. Because we are dividing both sides by a negative number, we reverse the inequality sign. 130 −44x ≥ −44 −44 Divide both sides by −44 and reverse the inequality sign. 65 x≥− 22 Simplify both sides. Shade all real numbers that are “greater than or equal to” or “right of or including” −65/22 on a number line. −65/22 Thus, using set-builder and interval notation, the solution is: {x : x ≥ −65/22} = [−65/22, ∞) Second Edition: 2012-2013 2.6. INEQUALITIES 123 75. The common denominator is 14. Clear the fractions from the inequality by multiplying both sides of the inequality by 14. 9 9 1 7 x+ > x+ 2 7 2 7 9 9 1 7 14 x+ > x+ 14 7 2 7 2 18x + 63 > 2x + 49 Original inequality. Multiply both sides by 14. Cancel and multiply. We need to isolate all terms containing x on one side of the equation. To “undo” adding 2x, subtract 2x from both sides of the inequality. 18x + 63 − 2x > 2x + 49 − 2x Subtract 2x from both sides. 16x + 63 > 49 Simplify both sides. We continue to isolate terms containing x on one side of the inequality. To “undo” adding 63, subtract 63 from both sides of the inequality. 16x + 63 − 63 > 49 − 63 Subtract 63 from both sides. 16x > −14 Simplify both sides. To “undo” the eﬀect of multiplying by 16, divide both sides of the inequality by 16. Because we are dividing both sides by a positive number, we do not reverse the inequality sign. 16x −14 > 16 16 7 x>− 8 Divide both sides by 16. Simplify both sides. Shade all real numbers that are “greater than” or “right of” −7/8 on a number line. −7/8 Thus, using set-builder and interval notation, the solution is: {x : x > −7/8} = (−7/8, ∞) Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 124 77. We’ll ﬁrst clear the decimals by multiplying both sides by 100, which will move each decimal point two places to the right. −3.7x − 1.98 ≤ 3.2 −370x − 198 ≤ 320 Original inequality. Multiply both sides by 100. To “undo” subtracting 198, add 198 to both sides of the inequality. −370x − 198 + 198 ≤ 320 + 198 −370x ≤ 518 Add 198 to both sides. Simplify both sides. To “undo” multiplying by −370, divide both sides of the inequality by −370. Because we are dividing by a negative number, so we reverse the inequality sign. −370x 518 ≥ −370 −370 7 x≥− 5 Simplify both sides. Reduce to lowest terms. Shade all real numbers that are “greater than or equal to” or “right of or including” −7/5 on a number line. −7/5 Thus, using set-builder and interval notation, the solution is: {x : x ≥ −7/5} = [−7/5, ∞) 79. We’ll ﬁrst clear the decimals by multiplying both sides by 10, which will move each decimal point one place to the right. −3.4x + 3.5 ≥ 0.9 − 2.2x −34x + 35 ≥ 9 − 22x Original inequality. Multiply both sides by 10. We need to isolate terms containing x on one side of the inequality. Start by adding 22x to both sides of the inequality. −34x + 35 + 22x ≥ 9 − 22x + 22x −12x + 35 ≥ 9 Add 22x to both sides. Simplify both sides. We continue to isolate terms containing x on one side of the inequality. Subtract 35 from both sides of the inequality. −12x + 35 − 35 ≥ 9 − 35 −12x ≥ −26 Second Edition: 2012-2013 Subtract 35 from both sides. Simplify both sides. 2.6. INEQUALITIES 125 To “undo” multiplying by −12, divide both sides of the inequality by −12. Because we are dividing by a negative number, we reverse the inequality sign. −12x −26 ≤ −12 −12 13 x≤ 6 Simplify both sides. Reduce to lowest terms. Shade all real numbers that are “less than or equal” or “left of or including ” 13/6 on a number line. 13/6 Thus, using set-builder and interval notation, the solution is: {x : x ≤ 13/6} = (−∞, 13/6] 81. We’ll ﬁrst clear the decimals by multiplying both sides by 10, which will move each decimal point one place to the right. −1.3x + 2.9 > −2.6 − 3.3x −13x + 29 > −26 − 33x Original inequality. Multiply both sides by 10. We need to isolate terms containing x on one side of the inequality. Start by adding 33x to both sides of the inequality. −13x + 29 + 33x > −26 − 33x + 33x 20x + 29 > −26 Add 33x to both sides. Simplify both sides. We continue to isolate terms containing x on one side of the inequality. Subtract 29 from both sides of the inequality. 20x + 29 − 29 > −26 − 29 20x > −55 Subtract 29 from both sides. Simplify both sides. To “undo” multiplying by 20, divide both sides of the inequality by 20. Because we are dividing by a positive number, we do not reverse the inequality sign. −55 20x > 20 20 11 x>− 4 Simplify both sides. Reduce to lowest terms. Shade all real numbers that are “greater than” or “right of ” −11/4 on a number line. Second Edition: 2012-2013 CHAPTER 2. SOLVING LINEAR EQUATIONS 126 −11/4 Thus, using set-builder and interval notation, the solution is: {x : x > −11/4} = (−11/4, ∞) 83. We’ll ﬁrst clear the decimals by multiplying both sides by 10, which will move each decimal point one place to the right. 2.2x + 1.9 < −2.3 22x + 19 < −23 Original inequality. Multiply both sides by 10. To “undo” adding 19, subtract 19 from both sides of the inequality. 22x + 19 − 19 < −23 − 19 22x < −42 Subtract 19 from both sides. Simplify both sides. To “undo” multiplying by 22, divide both sides of the inequality by 22. Because we are dividing by a positive number, we do not reverse the inequality sign. 22x −42 < 22 22 21 x<− 11 Simplify both sides. Reduce to lowest terms. Shade all real numbers that are “less than” or “left of ” −21/11 on a number line. −21/11 Thus, using set-builder and interval notation, the solution is: {x : x < −21/11} = (−∞, −21/11) Second Edition: 2012-2013 Chapter 3 Introduction to Graphing 3.1 Graphing Equations by Hand 1. To plot the point A(2, −4), move 2 units to the right, then move 4 units down. The remaining points are plotted in a similar manner. y y 5 5 C(−3, 2) 2 −5 5 x −5 5 −4 −5 B(−4, −3) A(2, −4) −5 A(2, −4) 3. To plot the point A(3, −2), move 3 units to the right, then move 2 units down. The remaining points are plotted in a similar manner. 127 x CHAPTER 3. INTRODUCTION TO GRAPHING 128 y y 5 5 C(−2, 3) 3 −5 −2 5 x −5 x 5 A(3, −2) A(3, −2) B(−3, −4) −5 −5 5. To plot the point A(−2, 2), move 2 units to the left, then move 2 units up. The remaining points are plotted in a similar manner. y y 5 5 A(−2, 2) A(−2, 2) 2 −5 −2 5 x −5 5 C(2, −2) B(−2, −3) −5 x −5 7. Start at the origin, move 4 units to the left then move 3 units up to reach the point P . y 5 P (−4, 3) 3 −5 −4 5 −5 Second Edition: 2012-2013 x 3.1. GRAPHING EQUATIONS BY HAND 129 9. Start at the origin, move 3 units to the right then move 4 units down to reach the point P . y 5 3 −5 5 x −4 P (3, −4) −5 11. Substitute (x, y) = (5, 20) into the equation y = 5x − 5. y = 5x − 5 Original equation. 20 = 5(5) − 5 Substitute: 5 for x, 20 for y. 20 = 25 − 5 20 = 20 Multiply: 5(5) = 25. Subtract: 25 − 5 = 20. Because this last statement is a true statement, (5, 20) satisﬁes (is a solution of) the equation y = 5x − 5. For contrast, consider the point (8, 36). y = 5x − 5 36 = 5(8) − 5 Original equation. Substitute: 8 for x, 36 for y. 36 = 40 − 5 36 = 35 Multiply: 5(8) = 40. Subtract: 40 − 5 = 35. Note that this last statement is false. Hence, the pair (8, 36) is not a solution of y = 5x − 5. In similar fashion, readers should also check that the remaining two points are not solutions. 13. Substitute (x, y) = (1, 1) into the equation y = −5x + 6. y = −5x + 6 Original equation. 1 = −5(1) + 6 1 = −5 + 6 Substitute: 1 for x, 1 for y. Multiply: −5(1) = −5. 1=1 Add: −5 + 6 = 1. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 130 Because this last statement is a true statement, (1, 1) satisﬁes (is a solution of) the equation y = −5x + 6. For contrast, consider the point (2, −3). y = −5x + 6 Original equation. −3 = −5(2) + 6 −3 = −10 + 6 Substitute: 2 for x, −3 for y. Multiply: −5(2) = −10. −3 = −4 Add: −10 + 6 = −4. Note that this last statement is false. Hence, the pair (2, −3) is not a solution of y = −5x+6. In similar fashion, readers should also check that the remaining two points are not solutions. 15. Substitute (x, y) = (7, 395) into the equation y = 8x2 + 3. y = 8x2 + 3 2 Original equation. 395 = 8(7) + 3 Substitute: 7 for x, 395 for y. 395 = 8(49) + 3 Square: (7)2 = 49. 395 = 392 + 3 395 = 395 Multiply: 8(49) = 392. Add: 392 + 3 = 395. Because this last statement is a true statement, (7, 395) satisﬁes (is a solution of) the equation y = 8x2 + 3. For contrast, consider the point (1, 12). y = 8x2 + 3 2 Original equation. 12 = 8(1) + 3 Substitute: 1 for x, 12 for y. 12 = 8(1) + 3 Square: (1)2 = 1. 12 = 8 + 3 12 = 11 Multiply: 8(1) = 8. Add: 8 + 3 = 11. Note that this last statement is false. Hence, the pair (1, 12) is not a solution of y = 8x2 + 3. In similar fashion, readers should also check that the remaining two points are not solutions. 17. Substitute (x, y) = (8, 400) into the equation y = 6x2 + 2x. y = 6x2 + 2x 2 Original equation. 400 = 6(8) + 2(8) Substitute: 8 for x, 400 for y. 400 = 6(64) + 2(8) 400 = 384 + 16 Square: (8)2 = 64. Multiply: 6(64) = 384; 2(8) = 16 400 = 400 Add: 384 + 16 = 400. Second Edition: 2012-2013 3.1. GRAPHING EQUATIONS BY HAND 131 Because this last statement is a true statement, (8, 400) satisﬁes (is a solution of) the equation y = 6x2 + 2x. For contrast, consider the point (2, 29). y = 6x2 + 2x Original equation. 2 29 = 6(2) + 2(2) Substitute: 2 for x, 29 for y. 29 = 6(4) + 2(2) 29 = 24 + 4 Square: (2)2 = 4. Multiply: 6(4) = 24; 2(2) = 4 29 = 28 Add: 24 + 4 = 28. Note that this last statement is false. Hence, the pair (2, 29) is not a solution of y = 6x2 + 2x. In similar fashion, readers should also check that the remaining two points are not solutions. 19. First, complete the table of points that satisfy the equation y = 2x + 1. y y y y y y y x −3 −2 −1 0 1 2 3 = 2(−3) + 1 = −5 = 2(−2) + 1 = −3 = 2(−1) + 1 = −1 = 2(0) + 1 = 1 = 2(1) + 1 = 3 = 2(2) + 1 = 5 = 2(3) + 1 = 7 y = 2x + 1 −5 −3 −1 1 3 5 7 (x, y) (−3, −5) (−2, −3) (−1, −1) (0, 1) (1, 3) (2, 5) (3, 7) Next, plot the points in the table, as shown in the image on the right. This ﬁrst image gives us enough evidence to believe that if we plotted all points satisfying the equation y = 2x + 1, the result would be the graph on the right. y y 10 −10 10 10 −10 x −10 y = 2x + 1 10 −10 Second Edition: 2012-2013 x CHAPTER 3. INTRODUCTION TO GRAPHING 132 21. First, complete the table of points that satisfy the equation y = |x − 5|. y y y y y y y x 2 3 4 5 6 7 8 = |2 − 5| = 3 = |3 − 5| = 2 = |4 − 5| = 1 = |5 − 5| = 0 = |6 − 5| = 1 = |7 − 5| = 2 = |8 − 5| = 3 y = |x − 5| 3 2 1 0 1 2 3 (x, y) (2, 3) (3, 2) (4, 1) (5, 0) (6, 1) (7, 2) (8, 3) Next, plot the points in the table, as shown in the image on the right. This ﬁrst image gives us enough evidence to believe that if we plotted all points satisfying the equation y = |x − 5|, the result would be the graph on the right. y y 10 10 y = |x − 5| −10 10 x −10 −10 10 −10 23. First, complete the table of points that satisfy the equation y = (x + 1)2 . y y y y y y y 2 = (−4 + 1) = 9 = (−3 + 1)2 = 4 = (−2 + 1)2 = 1 = (−1 + 1)2 = 0 = (0 + 1)2 = 1 = (1 + 1)2 = 4 = (2 + 1)2 = 9 x −4 −3 −2 −1 0 1 2 y = (x + 1)2 9 4 1 0 1 4 9 (x, y) (−4, 9) (−3, 4) (−2, 1) (−1, 0) (0, 1) (1, 4) (2, 9) Next, plot the points in the table, as shown in the image on the left. This ﬁrst image gives us enough evidence to believe that if we plotted all points Second Edition: 2012-2013 x 3.1. GRAPHING EQUATIONS BY HAND 133 satisfying the equation y = (x + 1)2 , the result would be the graph on the right. y y = (x + 1)2 10 −10 10 x y 10 −10 −10 10 −10 25. First, complete the table of points that satisfy the equation y = −x − 5. y y y y y y y = −(−3) − 5 = −2 = −(−2) − 5 = −3 = −(−1) − 5 = −4 = −(0) − 5 = −5 = −(1) − 5 = −6 = −(2) − 5 = −7 = −(3) − 5 = −8 x −3 −2 −1 0 1 2 3 y = −x − 5 −2 −3 −4 −5 −6 −7 −8 (x, y) (−3, −2) (−2, −3) (−1, −4) (0, −5) (1, −6) (2, −7) (3, −8) Next, plot the points in the table, as shown in the image on the right. This ﬁrst image gives us enough evidence to believe that if we plotted all points satisfying the equation y = −x − 5, the result would be the graph on the right. Second Edition: 2012-2013 x CHAPTER 3. INTRODUCTION TO GRAPHING 134 y y 10 10 −10 10 x −10 10 −10 −10 x y = −x − 5 27. Enter the equation y = x2 − 6x + 5 in Y1 in the Y= menu, using the following keystrokes. ∧ X,T,θ,n 2 − 6 × X,T,θ,n + 5 ENTER Press 2ND WINDOW, then set TblStart = 0 and ΔTbl = 1. Press 2ND GRAPH to produce the table. Enter the data from your calculator into a table on your graph paper. Use a ruler to construct the axes of your coordinate system, label and scale each axis. Plot the points in the table, as shown in the image on the right. y 10 x y (x, y) 0 1 2 3 4 5 6 5 0 −3 −4 −3 0 5 (0, 5) (1, 0) (2, −3) (3, −4) (4, −3) (5, 0) (6, 5) −10 10 −10 Second Edition: 2012-2013 x 3.1. GRAPHING EQUATIONS BY HAND 135 The plotted points provide enough evidence to convince us that if we plotted all points that satisﬁed the equation y = x2 −6x+5, we would get the following result. y 10 y = x2 − 6x + 5 −10 10 x −10 29. Enter the equation y = −x2 + 2x + 3 in Y1 in the Y= menu using the following keystrokes. (-) X,T,θ,n ∧ 2 + 2 × X,T,θ,n + 3 ENTER Press 2ND WINDOW, then set TblStart = −2 and ΔTbl = 1. Press 2ND GRAPH to produce the table. Enter the data from your calculator into a table on your graph paper. Use a ruler to construct the axes of your coordinate system, label and scale each axis. Plot the points in the table, as shown in the image on the right. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 136 y 10 x y (x, y) −2 −1 0 1 2 3 4 −5 0 3 4 3 0 −5 (−2, −5) (−1, 0) (0, 3) (1, 4) (2, 3) (3, 0) (4, −5) −10 10 x −10 The plotted points provide enough evidence to convince us that if we plotted all points that satisﬁed the equation y = −x2 +2x+3, we would get the following result. y 10 −10 10 x y = −x2 + 2x + 3 −10 31. Enter the equation y = x3 − 4x2 − 7x + 10 in Y1 in the Y= menu using the following keystrokes. X,T,θ,n ∧ 3 − × 4 + 1 X,T,θ,n 0 ∧ 2 − 7 × X,T,θ,n ENTER Press 2ND WINDOW, then set TblStart = −3 and ΔTbl = 1. Press 2ND GRAPH to produce the table. Second Edition: 2012-2013 3.1. GRAPHING EQUATIONS BY HAND 137 Enter the data from your calculator into a table on your graph paper. Use a ruler to construct the axes of your coordinate system, label and scale each axis. Plot the points in the table, as shown in the image on the right. y x y (x, y) −3 −2 −1 0 1 2 3 4 5 6 −32 0 12 10 0 −12 −20 −18 0 40 (−3, −32) (−2, 0) (−1, 12) (0, 10) (1, 0) (2, −12) (3, −20) (4, −18) (5, 0) (6, 40) 50 −10 10 −50 The plotted points provide enough evidence to convince us that if we plotted all points that satisﬁed the equation y = x3 − 4x2 − 7x + 10, we would get the following result. y 50 y = x3 − 4x2 − 7x + 10 −10 10 x −50 Second Edition: 2012-2013 x CHAPTER 3. INTRODUCTION TO GRAPHING 138 33. Enter the equation y = −x3 + 4x2 + 7x − 10 in Y1 in the Y= menu using the following keystrokes. (-) X,T,θ,n ∧ 3 + − × 4 1 0 X,T,θ,n ∧ 2 + 7 × ENTER Press 2ND WINDOW, then set TblStart = −3 and ΔTbl = 1. Press 2ND GRAPH to produce the table. Enter the data from your calculator into a table on your graph paper. Use a ruler to construct the axes of your coordinate system, label and scale each axis. Plot the points in the table, as shown in the image on the right. x y (x, y) −3 −2 −1 0 1 2 3 4 5 6 32 0 −12 −10 0 12 20 18 0 −40 (−3, 32) (−2, 0) (−1, −12) (0, −10) (1, 0) (2, 12) (3, 20) (4, 18) (5, 0) (6, −40) y 50 −10 10 −50 The plotted points provide enough evidence to convince us that if we plotted all points that satisﬁed the equation y = −x3 + 4x2 + 7x − 10, we would get the following result. Second Edition: 2012-2013 x X,T,θ,n 3.1. GRAPHING EQUATIONS BY HAND 139 y 50 −10 10 x y = −x3 + 4x2 + 7x − 10 −50 √ 35. First, enter the equation y = x + 5 into Y1 in the Y= menu using the following keystrokes. The results are shown in the ﬁrst image below. 2ND √ X,T,θ,n + 5) ENTER Next, select 2ND WINDOW and adjust the settings to match those in the second image. below. Finally, select 2ND GRAPH to open the TABLE. Copy the results from the third image below into the tables on your graph paper. x −5 −4 −3 −2 −1 0 1 2 y= √ x+5 0 1 1.4 1.7 2 2.2 2.4 2.6 (x, y) (−5, 0) (−4, 1) (−3, 1.4) (−2, 1.7) (−1, 2) (0, 2.2) (1, 2.4) (2, 2.6) x 3 4 5 6 7 8 9 10 y= √ x+5 2.8 3 3.2 3.3 3.5 3.6 3.7 3.9 (x, y) (3, 2.8) (4, 3) (5, 3.2) (6, 3.3) (7, 3.5) (8, 3.6) (9, 3.7) (10, 3.9) Next, plot the points in the tables, as shown in the image on the left. This ﬁrst image gives us enough√evidence to believe that if we plotted all points satisfying the equation y = x + 5, the result would be the graph on the right. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 140 y y 10 10 y= −10 10 x −10 −10 The Graphing Calculator 1. Enter the equation y = 2x + 3 into the Y= menu, then select 6:ZStandard from the ZOOM menu. Report the graph on your homework as follows: y y = 2x + 3 10 −10 10 −10 Second Edition: 2012-2013 x+5 10 −10 3.2 √ x x 3.2. THE GRAPHING CALCULATOR 141 3. Enter the equation y = 12 x−4 into the Y= menu, then select 6:ZStandard from the ZOOM menu. Report the graph on your homework as follows: y 10 −10 y = 12 x − 4 10 x −10 5. Enter the equation y = 9 − x2 into the Y= menu, then select 6:ZStandard from the ZOOM menu. Report the graph on your homework as follows: Second Edition: 2012-2013 142 CHAPTER 3. INTRODUCTION TO GRAPHING y 10 −10 10 −10 x y = 9 − x2 7. Enter the equation y = 12 x2 −3 into the Y= menu, then select 6:ZStandard from the ZOOM menu. Report the graph on your homework as follows: y y = 12 x2 − 3 10 −10 10 x −10 9. Enter the equation y = from the ZOOM menu. Second Edition: 2012-2013 √ x into the Y= menu, then select 6:ZStandard 3.2. THE GRAPHING CALCULATOR 143 Report the graph on your homework as follows: y 10 y= −10 √ 10 x x −10 √ 11. Enter the equation y = x + 3 into the Y= menu, then select 6:ZStandard from the ZOOM menu. Report the graph on your homework as follows: y 10 y= −10 √ x+3 10 x −10 13. Enter the equation y = |x| into the Y= menu, then select 6:ZStandard from the ZOOM menu. Second Edition: 2012-2013 144 CHAPTER 3. INTRODUCTION TO GRAPHING Report the graph on your homework as follows: y = |x| y 10 −10 10 x −10 15. Enter the equation y = |x+2| into the Y= menu, then select 6:ZStandard from the ZOOM menu. Report the graph on your homework as follows: y y = |x + 2| 10 −10 10 −10 Second Edition: 2012-2013 x 3.2. THE GRAPHING CALCULATOR 145 17. Enter the equation y = x2 + x − 20 into Y1= of the Y= menu, as shown in the ﬁrst image below, then select 6:ZStandard from the ZOOM menu. In the WINDOW menu, make the changes shown in the second image to Ymin and Ymax, then push the GRAPH button to produce the graph shown in the third image. Report the graph on your homework as follows: y y = x2 + x − 20 30 −10 10 x −30 19. Enter the equation y = −x2 +4x+21 into Y1= of the Y= menu, as shown in the ﬁrst image below, then select 6:ZStandard from the ZOOM menu. In the WINDOW menu, make the changes shown in the second image to Ymin and Ymax, then push the GRAPH button to produce the graph shown in the third image. Report the graph on your homework as follows: Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 146 y 30 −10 10 −30 x y = −x2 + 4x + 21 21. Enter the equation y = 2x2 −13x−24 into Y1= of the Y= menu, as shown in the ﬁrst image below, then select 6:ZStandard from the ZOOM menu. In the WINDOW menu, make the changes shown in the second image to Ymin and Ymax, then push the GRAPH button to produce the graph shown in the third image. Report the graph on your homework as follows: y y = 2x2 − 13x − 24 50 −10 10 x −50 23. Enter the equations y = 2x + 1 and y = x + 8 into Y1= and Y2= of the Y= menu, as shown in the ﬁrst image below, then select 6:ZStandard from the ZOOM menu. In the WINDOW menu, make the changes shown in Second Edition: 2012-2013 3.2. THE GRAPHING CALCULATOR 147 the second image to Ymin and Ymax, then push the GRAPH button. Press the TRACE button, then use the arrow keys to move the cursor as close as possible to the point of intersection, as shown in the third image. Report the graph on your homework as follows. As the TRACE key is only an approximation, estimates of the point of intersection may vary a bit. y 20 (6.91, 14.82) y =x+8 −5 y = 2x + 1 15 x −5 25. Enter the equations y = 12 x and y = 23 x−3 into Y1= and Y2= of the Y= menu, as shown in the ﬁrst image below, then select 6:ZStandard from the ZOOM menu. In the WINDOW menu, make the changes shown in the second image to Ymin and Ymax, then push the GRAPH button. Press the TRACE button, then use the arrow keys to move the cursor as close as possible to the point of intersection, as shown in the third image. Report the graph on your homework as follows. As the TRACE key is only an approximation, estimates of the point of intersection may vary a bit. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 148 y 20 (18.08, 9.04) y = 12 x x 35 −5 −5 y = 23 x − 3 27. Enter the equations y = 5 − x and y = −3 − 2x into Y1= and Y2= of the Y= menu, as shown in the ﬁrst image below, then select 6:ZStandard from the ZOOM menu. In the WINDOW menu, make the changes shown in the second image to Ymin and Ymax, then push the GRAPH button. Press the TRACE button, then use the arrow keys to move the cursor as close as possible to the point of intersection, as shown in the third image. Report the graph on your homework as follows. As the TRACE key is only an approximation, estimates of the point of intersection may vary a bit. y 25 (−7.76, 12.76) y = 5−x −25 5 −5 Second Edition: 2012-2013 x y = −3 − 2x 3.3. RATES AND SLOPE 3.3 149 Rates and Slope 1. Start by setting up a Cartesian Coordinate System, labeling and scaling each axis. Plot the point (0, 10). This represents the fact that the initial velocity is v = 10 m/s at time t = 0 s. Because the object accelerates at a rate of 5 m/s each second, start at the point (0,10), then every time you move 1 second to the right, move 5 m/s upward. Do this for 5 consecutive points. Finally, as evidenced from the initial points plotted on the left, the constant acceleration of 5 m/s/s guarantees that the graph of the object’s velocity versus time will be a line, shown on the right. v(m/s) v(m/s) 50 50 40 40 30 30 20 20 10 0 10 (0, 10) 0 1 2 3 4 5 6 7 8 9 10 t(s)0 (0, 10) 0 1 2 3 4 5 6 7 8 9 10 We know that every time the time increases by 1 second (Δt = 1 s), the object’s speed increases by 5 m/s (Δv = 5 m/s). Thus, the slope of the line is: Δv Δt 5 m/s = 1s = 5 m/s/s Slope = Note that the slope of the line is identical to the rate at which the objects’s velocity is increasing with respect to time. 3. Start by setting up a Cartesian Coordinate System, labeling and scaling each axis. Plot the point (0, 90). This represents the fact that the David’s initial distance from his brother is d = 90 feet at time t = 0 seconds. Because David’s distance from his brother decreases at a constant rate of 10 feet per second (10 ft/s), start at the point (0,90), then every time you move 1 second to the right, move 10 ft downward. Do this for 5 consecutive points. Finally, Second Edition: 2012-2013 t(s) CHAPTER 3. INTRODUCTION TO GRAPHING 150 as evidenced from the initial points plotted on the left, the decrease of David’s distance from his brother at a constant rate of 10ft/s guarantees that the graph of the David’s distance from his brother versus time will be a line, shown on the right. d(ft) d(ft) 100 (0, 90) 100 (0, 90) 90 90 80 80 70 70 60 60 50 50 40 40 30 30 20 20 10 10 t(s)0 t(s) 0 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 We know that every time the time increases by 1 second (Δt = 1 s), David’s distance from his brother decreases by 10 ft (Δd = −10 ft). Thus, the slope of the line is: Δd Δt −10 ft = 1s = −10 ft/s Slope = Note that the slope of the line is identical to the rate at which the David’s distance from his brother is decreasing with respect to time. Note that the minus sign indicates the the David’s distance from his brother is decreasing with respect to time. 5. To calculate the slope, we’ll subtract the coordinates of point P (9, 0) from Second Edition: 2012-2013 3.3. RATES AND SLOPE 151 the point Q(−9, 15). Slope = = Δy Δx 15 − 0 −9 − 9 15 −18 5 =− 6 = Slope is the change in y divided by the change in x. Divide the diﬀerence in y by the diﬀerence in x. Simplify numerator and denominator. Reduce to lowest terms. 7. To calculate the slope, we’ll subtract the coordinates of point P (0, 11) from the point Q(16, −11). Slope = = Δy Δx −11 − 11 16 − 0 −22 16 11 =− 8 = Slope is the change in y divided by the change in x. Divide the diﬀerence in y by the diﬀerence in x. Simplify numerator and denominator. Reduce to lowest terms. 9. To calculate the slope, we’ll subtract the coordinates of point P (11, 1) from the point Q(−1, −1). Slope = = Δy Δx −1 − 1 −1 − 11 −2 −12 1 = 6 = Slope is the change in y divided by the change in x. Divide the diﬀerence in y by the diﬀerence in x. Simplify numerator and denominator. Reduce to lowest terms. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 152 11. To calculate the slope, we’ll subtract the coordinates of point P (−18, 8) from the point Q(3, −10). Slope = = Δy Δx Slope is the change in y divided by the change in x. −10 − 8 3 − (−18) −18 21 6 =− 7 = Divide the diﬀerence in y by the diﬀerence in x. Simplify numerator and denominator. Reduce to lowest terms. 13. To calculate the slope, we’ll subtract the coordinates of point P (−18, 10) from the point Q(−9, 7). Slope = = Δy Δx Slope is the change in y divided by the change in x. 7 − 10 −9 − (−18) −3 9 1 =− 3 = Divide the diﬀerence in y by the diﬀerence in x. Simplify numerator and denominator. Reduce to lowest terms. 15. Because each gridline on the x-axis represents 1 unit, Δx = 8. Because each gridline on the y-axis represents 2 units, Δy = 12. y 20 Δy = 12 0 Δx = 8 0 Second Edition: 2012-2013 x 10 3.3. RATES AND SLOPE 153 Therefore, the slope is: Δy Δx 12 = 8 3 = 2 Slope = 17. Because each gridline on the x-axis represents 1 unit, Δx = 6. Because each gridline on the y-axis represents 2 units, Δy = −10. y 10 Δx = 6 x 5 Δy = −10 −5 −10 Therefore, the slope is: Δy Δx −10 = 6 5 =− 3 Slope = 19. First, sketch each of the lines passing through the given points. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 154 y 5 (0, 0) (1, 3) (1, 2) (1, 1) x −5 5 −5 Next, calculate the slope of each line. Slope through and (1, 1). (0, 0) Δy Δx 1−0 = 1−0 =1 Slope through and (1, 2). (0, 0) Slope through and (1, 3). Δy Δx 2−0 = 1−0 =2 m1 = Δy Δx 3−0 = 1−0 =3 m1 = m1 = Label each line with its slope. y 5 m3 = 3 m2 = 2 m1 = 1 x −5 5 −5 As the slope gets larger, the line gets steeper. Second Edition: 2012-2013 (0, 0) 3.3. RATES AND SLOPE 155 21. First, set up a coordinate system on a sheet of graph paper. Label and scale each axis, then plot the point P (−4, 0). Because the slope is Δy/Δx = −3/7, start at the point P (−4, 0), then move 3 units downward and 7 units to the right, reaching the point Q(3, −3). Draw the line through the points P and Q. y 5 P (−4, 0) −5 Δy = −3 5 x Q(3, −3) Δx = 7 −5 23. First, set up a coordinate system on a sheet of graph paper. Label and scale each axis, then plot the point P (−3, 0). Because the slope is Δy/Δx = 3/7, start at the point P (−3, 0), then move 3 units upward and 7 units to the right, reaching the point Q(4, 3). Draw the line through the points P and Q. y 5 Δx = 7 Q(4, 3) Δy = 3 −5 P (−3, 0) 5 x −5 25. First, set up a coordinate system on a sheet of graph paper. Label and scale each axis, then plot the point P (−3, −3). Because the slope is Δy/Δx = 3/7, start at the point P (−3, −3), then move 3 units upward and 7 units to the right, reaching the point Q(4, 0). Draw the line through the points P and Q. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 156 y 5 Δx = 7 x Q(4, 5 0) −5 Δy = 3 P (−3, −3) −5 27. First, set up a coordinate system on a sheet of graph paper. Label and scale each axis, then plot the point P (−4, 3). Because the slope is Δy/Δx = −3/5, start at the point P (−4, 3), then move 3 units downward and 5 units to the right, reaching the point Q(1, 0). Draw the line through the points P and Q. y 5 P (−4, 3) Δy = −3 Q(1, 0) −5 Δx = 5 5 x −5 29. First, set up a coordinate system on a sheet of graph paper. Label and scale each axis, then plot the point P (−1, 0). Because the slope is Δy/Δx = −3/4, start at the point P (−1, 0), then move 3 units downward and 4 units to the right, reaching the point Q(3, −3). Draw the line through the points P and Q. Second Edition: 2012-2013 3.4. SLOPE-INTERCEPT FORM OF A LINE 157 y 5 P (−1, 0) −5 5 x Δy = −3 Q(3, −3) Δx = 4 −5 3.4 Slope-Intercept Form of a Line 1. First, compare y = 95 x − 6 with y = mx + b and note that m = 9/5 and b = −6. Therefore, the slope of the line is 9/5 and the y-intercept is (0, −6). Next, set up a coordinate system on a sheet of graph paper. Label and scale each axis, then plot the y-intercept P (0, −6). Because the slope is Δy/Δx = 9/5, start at the y-intercept P (0, −6), then move 9 units upward and 5 units to the right, reaching the point Q(5, 3). Draw the line through the points P and Q and label it with its equation y = 95 x − 6. y y = 95 x − 6 10 Δx = 5 Q(5, 3) −10 10 Δy = 9 x P (0, −6) −10 3. First, compare y = − 11 4 x+ 4 with y = mx+ b and note that m = −11/4 and b = 4. Therefore, the slope of the line is −11/4 and the y-intercept is (0, 4). Next, set up a coordinate system on a sheet of graph paper. Label and scale each axis, then plot the y-intercept P (0, 4). Because the slope is Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 158 Δy/Δx = −11/4, start at the y-intercept P (0, 4), then move 11 units downward and 4 units to the right, reaching the point Q(4, −7). Draw the line through the points P and Q and label it with its equation y = − 11 4 x + 4. y 10 P (0, 4) −10 10 Δy = −11 x Q(4, −7) Δx = 4 x+4 y = − 11 4 −10 5. First, compare y = − 11 7 x+ 4 with y = mx+ b and note that m = −11/7 and b = 4. Therefore, the slope of the line is −11/7 and the y-intercept is (0, 4). Next, set up a coordinate system on a sheet of graph paper. Label and scale each axis, then plot the y-intercept P (0, 4). Because the slope is Δy/Δx = −11/7, start at the y-intercept P (0, 4), then move 11 units downward and 7 units to the right, reaching the point Q(7, −7). Draw the line through the points P and Q and label it with its equation y = − 11 7 x + 4. y 10 P (0, 4) −10 10 Δy = −11 x Q(7, −7) Δx = 7 −10 Second Edition: 2012-2013 x+4 y = − 11 7 3.4. SLOPE-INTERCEPT FORM OF A LINE 159 7. The y-intercept is (0, −7), so b = −7. Further, the slope is 9/5, so m = 9/5. Substitute these numbers into the slope-intercept form of the line. y = mx + b 9 y = x−7 5 Slope-intercept form. Substitute: 9/5 for m, −7 for b. Therefore, the slope-intercept form of the line is y = 95 x − 7. Next, set up a coordinate system on a sheet of graph paper. Label and scale each axis, then plot the y-intercept P (0, −7). Because the slope is Δy/Δx = 9/5, start at the y-intercept P (0, −7), then move 9 units upward and 5 units to the right, reaching the point Q(5, 2). Draw the line through the points P and Q and label it with its equation y = 95 x − 7. y y = 95 x − 7 10 Δx = 5 Q(5, 2) −10 10 x Δy = 9 P (0, −7) −10 9. The y-intercept is (0, −1), so b = −1. Further, the slope is 6/7, so m = 6/7. Substitute these numbers into the slope-intercept form of the line. y = mx + b 6 y = x−1 7 Slope-intercept form. Substitute: 6/7 for m, −1 for b. Therefore, the slope-intercept form of the line is y = 67 x − 1. Next, set up a coordinate system on a sheet of graph paper. Label and scale each axis, then plot the y-intercept P (0, −1). Because the slope is Δy/Δx = 6/7, start at the y-intercept P (0, −1), then move 6 units upward and 7 units to the right, reaching the point Q(7, 5). Draw the line through the points P and Q and label it with its equation y = 67 x − 1. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 160 y 10 y = 67 x − 1 Δx = 7 Q(7, 5) Δy = 6 −10 P (0, −1) 10 x −10 11. The y-intercept is (0, −6), so b = −6. Further, the slope is 9/7, so m = 9/7. Substitute these numbers into the slope-intercept form of the line. y = mx + b 9 y = x−6 7 Slope-intercept form. Substitute: 9/7 for m, −6 for b. Therefore, the slope-intercept form of the line is y = 97 x − 6. Next, set up a coordinate system on a sheet of graph paper. Label and scale each axis, then plot the y-intercept P (0, −6). Because the slope is Δy/Δx = 9/7, start at the y-intercept P (0, −6), then move 9 units upward and 7 units to the right, reaching the point Q(7, 3). Draw the line through the points P and Q and label it with its equation y = 97 x − 6. y 10 y = 97 x − 6 Δx = 7 −10 Q(7, 3) x 10 Δy = 9 P (0, −6) −10 Second Edition: 2012-2013 3.4. SLOPE-INTERCEPT FORM OF A LINE 161 13. First, note that the y-intercept of the line (where it crosses the y-axis) is the point P (0, 0). This means that b = 0 in the slope-intercept formula y = mx + b. Next, we need to determine the slope of the line. Try to locate a second point on the line that passes directly through a lattice point, a point where a horizontal and vertical gridline intersect. It appears that the point Q(3, −4) qualiﬁes. y 6 Subtract the coordinates of P (0, 0) from the coordinates of Q(3, −4) to determine the slope: P (0, 0) −6 Δy Δx −4 − (0) = 3−0 4 =− 3 m= x 6 Q(3, −4) −6 Alternate technique for finding the slope: Start at the y-intercept P (0, 0), then move 4 units downward and 3 units to the right, reaching the point Q(3, −4). y 6 P (0, 0) −6 6 x Δy = −4 Q(3, −4) Δx = 3 −6 This also indicates that the slope of the line is: Δy Δx −4 = 3 m= Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 162 Finally, substitute m = −4/3 and b = 0 in the slope-intercept form of the line: y = mx + b 4 y = − x + (0) 3 Hence, the equation of the line is y = − 34 x. 15. First, note that the y-intercept of the line (where it crosses the y-axis) is the point P (0, 1). This means that b = 1 in the slope-intercept formula y = mx + b. Next, we need to determine the slope of the line. Try to locate a second point on the line that passes directly through a lattice point, a point where a horizontal and vertical gridline intersect. It appears that the point Q(4, −4) qualiﬁes. y 6 Subtract the coordinates of P (0, 1) from the coordinates of Q(4, −4) to determine the slope: P (0, 1) −6 6 x Q(4, −4) Δy Δx −4 − 1 = 4−0 5 =− 4 m= −6 Alternate technique for finding the slope: Start at the y-intercept P (0, 1), then move 5 units downward and 4 units to the right, reaching the point Q(4, −4). Second Edition: 2012-2013 3.4. SLOPE-INTERCEPT FORM OF A LINE 163 y 6 P (0, 1) −6 6 Δy = −5 x Q(4, −4) Δx = 4 −6 This also indicates that the slope of the line is: Δy Δx −5 = 4 m= Finally, substitute m = −5/4 and b = 1 in the slope-intercept form of the line: y = mx + b 5 y =− x+1 4 Hence, the equation of the line is y = − 54 x + 1. 17. First, note that the y-intercept of the line (where it crosses the y-axis) is the point P (0, 0). This means that b = 0 in the slope-intercept formula y = mx + b. Next, we need to determine the slope of the line. Try to locate a second point on the line that passes directly through a lattice point, a point where a horizontal and vertical gridline intersect. It appears that the point Q(4, −3) qualiﬁes. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 164 y 6 Subtract the coordinates of P (0, 0) from the coordinates of Q(4, −3) to determine the slope: P (0, 0) −6 Δy Δx −3 − (0) = 4−0 3 =− 4 m= x 6 Q(4, −3) −6 Alternate technique for finding the slope: Start at the y-intercept P (0, 0), then move 3 units downward and 4 units to the right, reaching the point Q(4, −3). y 6 P (0, 0) −6 6 Δy = −3 x Q(4, −3) Δx = 4 −6 This also indicates that the slope of the line is: Δy Δx −3 = 4 m= Finally, substitute m = −3/4 and b = 0 in the slope-intercept form of the line: y = mx + b 3 y = − x + (0) 4 Hence, the equation of the line is y = − 43 x. Second Edition: 2012-2013 3.4. SLOPE-INTERCEPT FORM OF A LINE 165 19. First, note that the y-intercept of the line (where it crosses the y-axis) is the point P (0, −4). This means that b = −4 in the slope-intercept formula y = mx + b. Next, we need to determine the slope of the line. Try to locate a second point on the line that passes directly through a lattice point, a point where a horizontal and vertical gridline intersect. It appears that the point Q(5, 0) qualiﬁes. y 6 Subtract the coordinates of P (0, −4) from the coordinates of Q(5, 0) to determine the slope: Δy Δx 0 − (−4) = 5−0 4 = 5 m= x 6 0) Q(5, −6 P (0, −4) −6 Alternate technique for finding the slope: Start at the y-intercept P (0, −4), then move 4 units upward and 5 units to the right, reaching the point Q(5, 0). y 6 Δx = 5 −6 x 6 0) Q(5, Δy = 4 P (0, −4) −6 This also indicates that the slope of the line is: Δy Δx 4 = 5 m= Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 166 Finally, substitute m = 4/5 and b = −4 in the slope-intercept form of the line: y = mx + b 4 y = x + (−4) 5 Hence, the equation of the line is y = 45 x − 4. 21. Set up a coordinate system. Label the horizontal axis with the time t (in seconds) and the vertical axis with the velocity v (in meters per second). At time t = 0, the initial velocity is 20 m/s. This gives us the point (0,20). The velocity is increasing at a rate of 5 m/s each second. Let’s start at the point (0,20), then move right 10 seconds and upward 50 m/s, arriving at the point (10,70). Draw the line through these two points. Note that this makes the slope Δv/Δt = (50 m/s)/(10 s), or 2 m/s per second. v (m/s) 100 50 Δy = 50 (0, 20) 0 Δx = 10 0 10 20 t (s) Because we know the intercept is (0,20) and the slope is 5, we use the slope-intercept form to produce the equation of the line. y = mx + b Slope-intercept form. y = 5x + 20 Substitute: 5 for m, 20 for b. Replace y with v and x with t to produce the following result: v = 5t + 20 To ﬁnd the velocity at time t = 14 seconds, substitute 14 for t and simplify. v = 5(14) + 20 v = 90 Thus, at t = 14 seconds, the velocity is v = 90 m/s. Second Edition: 2012-2013 3.4. SLOPE-INTERCEPT FORM OF A LINE 167 23. Set up a coordinate system. Label the horizontal axis with the time t (in minutes) and the vertical axis with the volume V (in gallons). At time t = 0, the initial volume of water is 100 gallons. This gives us the point (0,100). The volume of water is increasing at a rate of 25 gal/min. Start at the point (0,100), then move right 10 minutes and upward 250 gallons, arriving at the point (10,350). Draw the line through these two points. Note that this makes the slope ΔV /Δt = (250 gal)/(10 min), or 25 gal/min, as required. v (gal) 1,000 500 Δy = 250 (0, 100) 0 Δx = 10 0 10 20 t (min) Because we know the intercept is (0,100) and the slope is 25, we use the slope-intercept form to produce the equation of the line. y = mx + b Slope-intercept form. y = 25x + 100 Substitute: 25 for m, 100 for b. Replace y with V and x with t to produce the following result: V = 25t + 100 To ﬁnd the time it takes the volume of water to reach 400 gallons, substitute 400 for V and solve for t. 400 = 25t + 100 400 − 100 = 25t + 100 − 100 300 = 25t 300 25t = 25 25 12 = t Substitute 400 for V . Subtract 100 from both sides. Simplify. Divide both sides by 25. Simplify. Thus, it takes 12 minutes for the volume of water to reach 400 gallons. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 168 3.5 Point-Slope Form of a Line 1. First, plot the point P (−3, 4). Then, because the slope is Δy/Δx = −5/7, start at the point P (−3, 4), then move 5 units downward and 7 units to the right, arriving at the point Q(4, −1). y 6 P (−3, 4) Δy = −5 x Q(4, −1) 6 −6 Δx = 7 −6 Next, substitute m = −5/7 and (x0 , y0 ) = (−3, 4) in the point-slope form of the line: y − y0 = m(x − x0 ) 5 y − 4 = − (x − (−3)) 7 Point-slope form. Substitute: −5/7 for m, −3 for x0 , and 4 for y0 Hence, the equation of the line is y − 4 = − 75 (x + 3). Label the line with its equation. y 6 P (−3, 4) Δy = −5 x Q(4, −1) 6 −6 Δx = 7 −6 Second Edition: 2012-2013 y − 4 = − 75 (x + 3) 3.5. POINT-SLOPE FORM OF A LINE 169 3. First, plot the point P (−2, 4). Then, because the slope is Δy/Δx = −4/5, start at the point P (−2, 4), then move 4 units downward and 5 units to the right, arriving at the point Q(3, 0). y 6 P (−2, 4) Δy = −4 Q(3, 0) −6 6 Δx = 5 x −6 Next, substitute m = −4/5 and (x0 , y0 ) = (−2, 4) in the point-slope form of the line: y − y0 = m(x − x0 ) 4 y − 4 = − (x − (−2)) 5 Point-slope form. Substitute: −4/5 for m, −2 for x0 , and 4 for y0 Hence, the equation of the line is y − 4 = − 45 (x + 2). Label the line with its equation. y 6 P (−2, 4) Δy = −4 Q(3, 0) −6 Δx = 5 6 x y − 4 = − 54 (x + 2) −6 5. First, plot the point P (−1, −4). Then, because the slope is Δy/Δx = 5/3, start at the point P (−1, −4), then move 5 units upward and 3 units to the right, arriving at the point Q(2, 1). Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 170 y 6 Δx = 3 −6 Q(2, 1) 6 x Δy = 5 P (−1, −4) −6 Next, substitute m = 5/3 and (x0 , y0 ) = (−1, −4) in the point-slope form of the line: y − y0 = m(x − x0 ) 5 y − (−4) = (x − (−1)) 3 Point-slope form. Substitute: 5/3 for m, −1 for x0 , and −4 for y0 Hence, the equation of the line is y + 4 = equation. 5 3 (x + 1). Label the line with its y y + 4 = 53 (x + 1) 6 Δx = 3 −6 Q(2, 1) 6 x Δy = 5 P (−1, −4) −6 7. Plot the points P (−4, 0) and Q(4, 3) and draw a line through them. Second Edition: 2012-2013 3.5. POINT-SLOPE FORM OF A LINE 171 y 6 Subtract the coordinates of poing P (−4, 0) from the point Q(4, 3). Q(4, 3) Δy Δx 3 − (0) = 4 − (−4) 3 = 8 m= −6 P (−4, 0) 6 x −6 Next, substitute m = 3/8, then substitute either point P (−4, 0) or point Q(4, 3) for (x0 , y0 ) in the point-slope form of the line. We’ll substitute P (−4, 0) for (x0 , y0 ). y − y0 = m(x − x0 ) 3 y − (0) = (x − (−4)) 8 Point-slope form. Substitute: 3/8 for m, −4 for x0 , and 0 for y0 Hence, the equation of the line is y = 38 (x+4). Label the line with its equation. y 6 y = 38 (x + 4) Q(4, 3) −6 P (−4, 0) 6 x −6 Alternately, if you substitute the point Q(4, 3) for (x0 , y0 ) in the point-slope form y − y0 = m(x − x0 ), you get an equivalent equation y − 3 = 38 (x − 4). 9. Plot the points P (−3, −3) and Q(2, 0) and draw a line through them. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 172 y 6 Subtract the coordinates of poing P (−3, −3) from the point Q(2, 0). Δy Δx 0 − (−3) = 2 − (−3) 3 = 5 m= −6 Q(2, 0) 6 x P (−3, −3) −6 Next, substitute m = 3/5, then substitute either point P (−3, −3) or point Q(2, 0) for (x0 , y0 ) in the point-slope form of the line. We’ll substitute P (−3, −3) for (x0 , y0 ). y − y0 = m(x − x0 ) 3 y − (−3) = (x − (−3)) 5 Point-slope form. Substitute: 3/5 for m, −3 for x0 , and −3 for y0 Hence, the equation of the line is y + 3 = equation. 3 5 (x + 3). Label the line with its y 6 y + 3 = 35 (x + 3) −6 Q(2, 0) 6 x P (−3, −3) −6 Alternately, if you substitute the point Q(2, 0) for (x0 , y0 ) in the point-slope form y − y0 = m(x − x0 ), you get an equivalent equation y = 35 (x − 2). 11. Plot the points P (−3, 1) and Q(4, −4) and draw a line through them. Second Edition: 2012-2013 3.5. POINT-SLOPE FORM OF A LINE 173 y 6 Subtract the coordinates of poing P (−3, 1) from the point Q(4, −4). P (−3, 1) Δy Δx −4 − 1 = 4 − (−3) 5 =− 7 m= −6 6 x Q(4, −4) −6 Next, substitute m = −5/7, then substitute either point P (−3, 1) or point Q(4, −4) for (x0 , y0 ) in the point-slope form of the line. We’ll substitute P (−3, 1) for (x0 , y0 ). y − y0 = m(x − x0 ) 5 y − 1 = − (x − (−3)) 7 Point-slope form. Substitute: −5/7 for m, −3 for x0 , and 1 for y0 Hence, the equation of the line is y − 1 = − 57 (x + 3). Label the line with its equation. y 6 P (−3, 1) −6 6 x Q(4, −4) −6 y − 1 = − 57 (x + 3) Alternately, if you substitute the point Q(4, −4) for (x0 , y0 ) in the point-slope form y − y0 = m(x − x0 ), you get an equivalent equation y + 4 = − 57 (x − 4). 13. Start by plotting the line y = − 45 x + 1. Comparing this equation with the slope-intercept form y = mx + b, we note that m = −5/4 and b = 1. Thus, Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 174 the slope is −5/4 and the y-intercept is (0, 1). First plot the y-intercept (0, 1). Because the slope is Δy/Δx = −5/4, start at the y-intercept, then move −5 units downward and 4 units to the right, arriving at the point (4, −4). Draw the line y = − 45 x + 1 through these two points. Next, plot the point P (−3, 2). Because the line through P must be parallel to the ﬁrst line, it must have the same slope −5/4. Start at the point P (−3, 2), then move −5 units downward and 4 units to the right, arriving at the point Q(1, −3). Draw the line through these two points. y = − 54 x + 1 y y = − 54 x + 1 6 y 6 P (−3, 2) (0, 1) −6 6 Δy = −5 x Δy −6 = −5 (4, −4) 6 Q(1, −3) Δx = 4 Δx = 4 −6 −6 To ﬁnd the equation of the second line, we’ll substitute the point (x0 , y0 ) = (−3, 2) and slope m = −5/4 into the point-slope form of the line. y − y0 = m(x − x0 ) 5 y − 2 = − (x − (−3)) 4 Point-slope form. Substitute: −5/4 for m, −3 for x0 , and 2 for y0 . Hence, the equation of the line is y − 2 = − 45 (x + 3). Label the line with its equation. Second Edition: 2012-2013 x 3.5. POINT-SLOPE FORM OF A LINE 175 y y = − 54 x + 1 6 P (−3, 2) −6 6 −6 x y − 2 = − 54 (x + 3) 15. Start by plotting the line y = 35 x. Comparing this equation with the slope-intercept form y = mx + b, we note that m = 3/5 and b = 0. Thus, the slope is 3/5 and the y-intercept is (0, 0). First plot the y-intercept (0, 0). Because the slope is Δy/Δx = 3/5, start at the y-intercept, then move 3 units upward and 5 units to the right, arriving at the point (5, 3). Draw the line y = 35 x through these two points. Next, plot the point P (−4, 0). Because the line through P must be parallel to the ﬁrst line, it must have the same slope 3/5. Start at the point P (−4, 0), then move 3 units upward and 5 units to the right, arriving at the point Q(1, 3). Draw the line through these two points. y y 6 6 Δx = 5 Δx = 5 Q(1, 3) (5, 3) Δy = 3 −6 Δy = 3 (0, 0) y = 35 x 6 x −6 P (−4, 0) 6 y = 35 x −6 −6 To ﬁnd the equation of the second line, we’ll substitute the point (x0 , y0 ) = Second Edition: 2012-2013 x CHAPTER 3. INTRODUCTION TO GRAPHING 176 (−4, 0) and slope m = 3/5 into the point-slope form of the line. y − y0 = m(x − x0 ) 3 y − 0 = (x − (−4)) 5 Point-slope form. Substitute: 3/5 for m, −4 for x0 , and 0 for y0 . Hence, the equation of the line is y = 35 (x+4). Label the line with its equation. y y = 35 (x + 4) 6 −6 P (−4, 0) 6 x y = 35 x −6 17. Start by plotting the line y = 34 x + 1. Comparing this equation with the slope-intercept form y = mx + b, we note that m = 3/4 and b = 1. Thus, the slope is 3/4 and the y-intercept is (0, 1). First plot the y-intercept (0, 1). Because the slope is Δy/Δx = 3/4, start at the y-intercept, then move 3 units upward and 4 units to the right, arriving at the point (4, 4). Draw the line y = 34 x + 1 through these two points. Next, plot the point P (−3, 0). Because the line through P must be parallel to the ﬁrst line, it must have the same slope 3/4. Start at the point P (−3, 0), then move 3 units upward and 4 units to the right, arriving at the point Q(1, 3). Draw the line through these two points. Second Edition: 2012-2013 3.5. POINT-SLOPE FORM OF A LINE 177 y y 6 6 Δx = 4 Δx = 4 (4, 4) Δy = 3 Q(1, 3) Δy = 3 (0, 1) −6 6 x y = 34 x + 1 −6 P (−3, 0) 6 x y = 34 x + 1 −6 −6 To ﬁnd the equation of the second line, we’ll substitute the point (x0 , y0 ) = (−3, 0) and slope m = 3/4 into the point-slope form of the line. y − y0 = m(x − x0 ) 3 y − 0 = (x − (−3)) 4 Point-slope form. Substitute: 3/4 for m, −3 for x0 , and 0 for y0 . Hence, the equation of the line is y = 34 (x+3). Label the line with its equation. y 6 −6 P (−3, 0) y = 34 (x + 3) 6 x y = 34 x + 1 −6 19. Start by plotting the line passing through the points P (−2, 0) and Q(2, −3) and then calculating its slope. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 178 y 6 Subtract coordinates of point P (−2, 0) from the coordinates of the point Q(2, −3). P (−2, 0) −6 6 x Q(2, −3) Δy Δx −3 − (0) = 2 − (−2) 3 =− 4 m= −6 Thus, the slope of the line through points P and Q is −3/4. The slope of any line perpendicular to this line is the negative reciprocal of this number, that is 4/3. The next step is to plot the point R(−1, 0). To draw a line through R with slope 4/3, start at the point R, then move upward 4 units and right 3 units, arriving at the point X(2, 4). y 6 Δx = 3 To ﬁnd the equation of the perpendicular line, substitute 4/3 for m and (−1, 0) for (x0 , y0 ) in the pointslope form. X(2, 4) Δy = 4 −6 R(−1, 0) 6 x y − y0 = m(x − x0 ) 4 y − (0) = (x − (−1)) 3 −6 Hence, the equation line through the point R perpendicular to the line through points P and Q is y = 43 (x + 1). Label the line with its equation. Second Edition: 2012-2013 3.5. POINT-SLOPE FORM OF A LINE 179 y y = 43 (x + 1) 6 −6 R(−1, 0) 6 x −6 21. Start by plotting the line passing through the points P (−2, −4) and Q(1, 4) and then calculating its slope. y 6 Subtract coordinates of point P (−2, −4) from the coordinates of the point Q(1, 4). Q(1, 4) −6 6 P (−2, −4) x Δy Δx 4 − (−4) = 1 − (−2) 8 = 3 m= −6 Thus, the slope of the line through points P and Q is 8/3. The slope of any line perpendicular to this line is the negative reciprocal of this number, that is −3/8. The next step is to plot the point R(−4, −1). To draw a line through R with slope −3/8, start at the point R, then move downward 3 units and right 8 units, arriving at the point X(4, −4). Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 180 y 6 To ﬁnd the equation of the perpendicular line, substitute −3/8 for m and (−4, −1) for (x0 , y0 ) in the point-slope form. −6 R(−4, −1) 6 Δy = −3 x y − y0 = m(x − x0 ) 3 y − (−1) = − (x − (−4)) 8 X(4, −4) Δx = 8 −6 Hence, the equation line through the point R perpendicular to the line through points P and Q is y + 1 = − 38 (x + 4). Label the line with its equation. y 6 −6 R(−4, −1) −6 6 x y + 1 = − 38 (x + 4) 23. Start by plotting the line passing through the points P (−2, 3) and Q(1, −1) and then calculating its slope. Second Edition: 2012-2013 3.5. POINT-SLOPE FORM OF A LINE 181 y 6 Subtract coordinates of point P (−2, 3) from the coordinates of the point Q(1, −1). P (−2, 3) −6 6 x Q(1, −1) Δy Δx −1 − 3 = 1 − (−2) 4 =− 3 m= −6 Thus, the slope of the line through points P and Q is −4/3. The slope of any line perpendicular to this line is the negative reciprocal of this number, that is 3/4. The next step is to plot the point R(−3, −4). To draw a line through R with slope 3/4, start at the point R, then move upward 3 units and right 4 units, arriving at the point X(1, −1). y 6 To ﬁnd the equation of the perpendicular line, substitute 3/4 for m and (−3, −4) for (x0 , y0 ) in the point-slope form. −6 Δx = 4 6 X(1, −1) Δy = 3 x y − y0 = m(x − x0 ) 3 y − (−4) = (x − (−3)) 4 R(−3, −4) −6 Hence, the equation line through the point R perpendicular to the line through points P and Q is y + 4 = 34 (x + 3). Label the line with its equation. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 182 y 6 y + 4 = 34 (x + 3) −6 6 x R(−3, −4) −6 25. Set up a coordinate system, placing the time t on the horizontal axis and velocity v on the vertical axis. Label and scale each axis, including units in your labels. Plot the points (3, 50) and (14, 30) and draw a line through the points. v (ft/s) 100 80 60 (3, 50) 40 (14, 30) 20 t (s) 0 0 2 4 6 Compute the slope. 30 − 50 14 − 3 −20 = 11 Slope = Second Edition: 2012-2013 8 10 12 14 16 18 20 Substitute −20/11 for m and (3, 50) for (x0 , y0 ) in the point-slope form. y − y0 = m(x − x0 ) 20 y − 50 = − (x − 3) 11 3.6. STANDARD FORM OF A LINE 183 Replace x with t and y with v. v − 50 = − 20 (t − 3) 11 Point-slope form. Solve for v. 20 t+ 11 20 v − 50 + 50 = − t + 11 20 v =− t+ 11 v − 50 = − v=− 60 11 60 + 50 11 60 550 + 11 11 610 20 t+ 11 11 Distribute −20/11. Add 50 to both sides. On the left, simplify. On the right make equivalent fractions, with a common denominator. Simplify. If the time is 6 seconds, then: 610 20 (6) + 11 11 v = 44.5454545454545 v=− A calculator was used to approximate the last computation. Rounded to the nearest second, the velocity of the object is v = 44.5 seconds. 3.6 Standard Form of a Line 1. First, solve the equation 4x − 3y = 9 for y: 4x − 3y = 9 4x − 3y − 4x = 9 − 4x −3y = −4x + 9 −3y −4x + 9 = −3 −3 4 y = x−3 3 Standard form of line. Subtract 4x from both sides. Simplify. Divide both sides by −3. Distribute −3 and simplify. Therefore, the slope of the line is 4/3 and the y-intercept is (0, −3). To sketch the graph of the line, ﬁrst plot the y-intercept, then move upward 4 units and right 3 units, arriving at the point (3, 1). Draw the line through (0, −3) and (3, 1) and label it with its equation in slope-intercept form. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 184 y y = 43 x − 3 6 Δx = 3 (3, 1) −6 6 Δy = 4 x (0, −3) −6 3. First, solve the equation 3x − 2y = 6 for y: 3x − 2y = 6 Standard form of line. 3x − 2y − 3x = 6 − 3x −2y = −3x + 6 −3x + 6 −2y = −2 −2 3 y = x−3 2 Subtract 3x from both sides. Simplify. Divide both sides by −2. Distribute −2 and simplify. Therefore, the slope of the line is 3/2 and the y-intercept is (0, −3). To sketch the graph of the line, ﬁrst plot the y-intercept, then move upward 3 units and right 2 units, arriving at the point (2, 0). Draw the line through (0, −3) and (2, 0) and label it with its equation in slope-intercept form. y y = 32 x − 3 6 Δx = 2 −6 (2, 0) Δy = 3 (0, −3) −6 Second Edition: 2012-2013 6 x 3.6. STANDARD FORM OF A LINE 185 5. First, solve the equation 2x + 3y = 12 for y: 2x + 3y = 12 2x + 3y − 2x = 12 − 2x Standard form of line. Subtract 2x from both sides. 3y = −2x + 12 3y −2x + 12 = 3 3 2 y =− x+4 3 Simplify. Divide both sides by 3. Distribute 3 and simplify. Therefore, the slope of the line is −2/3 and the y-intercept is (0, 4). To sketch the graph of the line, ﬁrst plot the y-intercept, then move downward 2 units and right 3 units, arriving at the point (3, 2). Draw the line through (0, 4) and (3, 2) and label it with its equation in slope-intercept form. y 6 (0, 4) Δy = −2 (3, 2) Δx = 3 x 6 y = − 32 x + 4 −6 −6 7. First, note that the y-intercept of the line (where it crosses the y-axis) is the point P (0, 0). This means that b = 0 in the slope-intercept formula y = mx+ b. Next, we need to determine the slope of the line. Try to locate a second point on the line that passes directly through a lattice point, a point where a horizontal and vertical gridline intersect. It appears that the point Q(5, −4) qualiﬁes. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 186 y 6 Subtract the coordinates of P (0, 0) from the coordinates of Q(5, −4) to determine the slope: P ((0, 0) −6 6 Δy Δx −4 − (0) = 5−0 4 =− 5 m= x Q(5, −4) −6 Finally, substitute m = −4/5 and b = 0 in the slope-intercept form of the line: y = mx + b 4 y = − x + (0) 5 Hence, the equation of the line in slope-intercept form is y = − 45 x. Standard form Ax+By = C does not allow fractional coeﬃcients. Thus, to put this equation into standard form, we must ﬁrst clear the fractions from the equation by multiplying both sides of the equation by the least common denominator. 4 y=− x 5 4 5y = − x 5 5 5y = −4x 5y + 4x = −4x + 4x 4x + 5y = 0 Slope-intercept form. Multiply both sides by 5. Distribute 5 and simplify. Add 4x from both sides. Simplify. Thus, the standard form of the line is 4x + 5y = 0. 9. First, note that the y-intercept of the line (where it crosses the y-axis) is the point P (0, −3). This means that b = −3 in the slope-intercept formula y = mx + b. Next, we need to determine the slope of the line. Try to locate a second point on the line that passes directly through a lattice point, a point where a horizontal and vertical gridline intersect. It appears that the point Q(5, −1) qualiﬁes. Second Edition: 2012-2013 3.6. STANDARD FORM OF A LINE 187 y 6 Subtract the coordinates of P (0, −3) from the coordinates of Q(5, −1) to determine the slope: Q(5, −1) −6 6 Δy Δx −1 − (−3) = 5−0 2 = 5 m= x P ((0, −3) −6 Finally, substitute m = 2/5 and b = −3 in the slope-intercept form of the line: y = mx + b 2 y = x + (−3) 5 Hence, the equation of the line in slope-intercept form is y = 25 x − 3. Standard form Ax+By = C does not allow fractional coeﬃcients. Thus, to put this equation into standard form, we must ﬁrst clear the fractions from the equation by multiplying both sides of the equation by the least common denominator. 2 x−3 5 2 5y = x−3 5 5 y= 5y = 2x − 15 5y − 2x = 2x − 15 − 2x −2x + 5y = −15 Slope-intercept form. Multiply both sides by 5. Distribute 5 and simplify. Subtract 2x from both sides. Simplify. Standard form Ax + By = C requires that A ≥ 0, so we multiply both sides by −1 to ﬁnish. −1 (−2x + 5y) = (−15)(−1) 2x − 5y = 15 Multiply both sides by −1. Distribute −1. Thus, the standard form of the line is 2x − 5y = 15. 11. First, plot the points P (−1, 4) and Q(2, −4) and draw a line through them. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 188 y 6 P (−1, 4) −6 6 x Q(2, −4) −6 Next, determine the slope then use the point-slope form to determine the equation of the line. Substitute −8/3 for m and (−1, 4) for (x0 , y0 ) in the point-slope form. Subtract the coordinates of the point P (−1, 4) from the coordinates of the point Q(2, −4). y − y0 = m(x − x0 ) 8 y − 4 = − (x − (−1)) 3 8 y − 4 = − (x + 1) 3 Δy m= Δx −4 − 4 = 2 − (−1) 8 =− 3 Next, we need to put y − 4 = − 83 (x + 1) into standard form. Standard form does not allow fractions as coeﬃcients, so the ﬁrst step is to clear fractions from the equation. 8 y − 4 = − (x + 1) 3 8 8 y−4=− x− 3 3 Clear fractions by multiplying both 8 3(y − 4) = − x − 3 3y − 12 = −8x − 8 8x + 3y = 4 Second Edition: 2012-2013 8 Distribute − . 3 sides by the least common denominator. 8 3 Multiply both sides by 3. 3 Distribute and simplify. 3y − 12 + 8x = −8x − 8 + 8x 8x + 3y − 12 = −8 8x + 3y − 12 + 12 = −8 + 12 Point-slope form. Add 8x to both sides. Simplify. Add 12 to both sides. 3.6. STANDARD FORM OF A LINE 189 Label the graph of the line with its equation in standard form. y 6 P (−1, 4) −6 6 x Q(2, −4) −6 8x + 3y = 4 13. First, plot the points P (−1, −1) and Q(3, 4) and draw a line through them. y 6 Q(3, 4) −6 6 x P (−1, −1) −6 Next, determine the slope then use the point-slope form to determine the equation of the line. Subtract the coordinates of the point P (−1, −1) from the coordinates of the point Q(3, 4). Δy m= Δx 4 − (−1) = 3 − (−1) 5 = 4 Substitute 5/4 for m and (−1, −1) for (x0 , y0 ) in the point-slope form. y − y0 = m(x − x0 ) 5 y − (−1) = (x − (−1)) 4 5 y + 1 = (x + 1) 4 Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 190 Next, we need to put y + 1 = 54 (x + 1) into standard form. Standard form does not allow fractions as coeﬃcients, so the ﬁrst step is to clear fractions from the equation. 5 (x + 1) 4 5 5 y+1= x+ 4 4 Point-slope form. y+1= Distribute 5 . 4 Clear fractions by multiplying both sides by the least common denominator. 4(y + 1) = 5 5 x+ 4 4 4 4y + 4 = 5x + 5 4y + 4 − 5x = 5x + 5 − 5x −5x + 4y + 4 = 5 −5x + 4y + 4 − 4 = 5 − 4 Multiply both sides by 4. Distribute and simplify. Subtract 5x to both sides. Simplify. Subtract 4 from both sides. −5x + 4y = 1 Simplify. Standard form Ax + By = C requires that A ≥ 0. Thus, we need to multiply both sides by −1 so that the coeﬃcient of x is greater than or equal to zero. −1(−5x + 4y) = (1)(−1) Multiply both sides by −1. 5x − 4y = −1 Simplify. Label the graph of the line with its equation in standard form. y 5x − 4y = −1 6 Q(3, 4) −6 6 x P (−1, −1) −6 15. First, plot the points P (−3, 1) and Q(2, −3) and draw a line through them. Second Edition: 2012-2013 3.6. STANDARD FORM OF A LINE 191 y 6 P (−3, 1) −6 6 x Q(2, −3) −6 Next, determine the slope then use the point-slope form to determine the equation of the line. Subtract the coordinates of the point P (−3, 1) from the coordinates of the point Q(2, −3). Δy m= Δx −3 − 1 = 2 − (−3) 4 =− 5 Substitute −4/5 for m and (−3, 1) for (x0 , y0 ) in the point-slope form. y − y0 = m(x − x0 ) 4 y − 1 = − (x − (−3)) 5 4 y − 1 = − (x + 3) 5 Next, we need to put y − 1 = − 54 (x + 3) into standard form. Standard form does not allow fractions as coeﬃcients, so the ﬁrst step is to clear fractions from the equation. 4 y − 1 = − (x + 3) 5 4 12 y−1=− x− 5 5 Point-slope form. 4 Distribute − . 5 Clear fractions by multiplying both sides by the least common denominator. 4 12 5(y − 1) = − x − 5 Multiply both sides by 5. 5 5 5y − 5 = −4x − 12 Distribute and simplify. 5y − 5 + 4x = −4x − 12 + 4x 4x + 5y − 5 = −12 4x + 5y − 5 + 5 = −12 + 5 Add 4x to both sides. Simplify. Add 5 to both sides. 4x + 5y = −7 Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 192 Label the graph of the line with its equation in standard form. y 6 P (−3, 1) −6 6 x Q(2, −3) −6 4x + 5y = −7 17. First, ﬁnd the x-and y-intercepts. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. 2x − 5y = 10 2x − 5y = 10 2x − 5(0) = 10 2(0) − 5y = 10 −5y = 10 −5y 10 = −5 −5 y = −2 2x = 10 2x 10 = 2 2 x=5 The y-intercept is (0, −2). The x-intercept is (5, 0). Plot the x- and y-intercepts, label them with their coordinates, then draw the line through them and label the line with its equation. y 6 2x − 5y = 10 x 6 0) (5, −6 (0, −2) −6 Second Edition: 2012-2013 3.6. STANDARD FORM OF A LINE 193 19. First, ﬁnd the x-and y-intercepts. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. 3x − 2y = 6 3x − 2(0) = 6 3x − 2y = 6 3(0) − 2y = 6 −2y = 6 −2y 6 = −2 −2 y = −3 3x = 6 3x 6 = 3 3 x=2 The y-intercept is (0, −3). The x-intercept is (2, 0). Plot the x- and y-intercepts, label them with their coordinates, then draw the line through them and label the line with its equation. y 3x − 2y = 6 6 −6 (2, 0) 6 x (0, −3) −6 21. First, ﬁnd the x-and y-intercepts. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. 2x + 3y = 6 2x + 3(0) = 6 2x + 3y = 6 2(0) + 3y = 6 2x = 6 2x 6 = 2 2 x=3 3y = 6 3y 6 = 3 3 y=2 The x-intercept is (3, 0). The y-intercept is (0, 2). Plot the x- and y-intercepts, label them with their coordinates, then draw the line through them and label the line with its equation. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 194 y 6 (0, 2) (3, 0) −6 6 x 2x + 3y = 6 −6 23. A sketch will help maintain our focus. First, determine the x- and yintercepts of 4x + 5y = −20. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. 4x + 5y = −20 4x + 5y = −20 4x + 5(0) = −20 4x = −20 −20 4x = 4 4 x = −5 4(0) + 5y 5y 5y 5 y = −20 = −20 −20 = 5 = −4 The y-intercept is (0, −4). The x-intercept is (−5, 0). Plot the x- and y-intercepts, label them with their coordinates, then draw the line through them and label the line with its equation. y 6 Use the intercepts (−5, 0) and (0, −4) to determine the slope. Pick a direction to subtract and stay consistent. (−5, 0) −6 6 (0, −4) −6 4x + 5y = −20 Second Edition: 2012-2013 x Δy Δx 0 − (−4) = −5 − 0 4 =− 5 m= 3.6. STANDARD FORM OF A LINE 195 Because the line 4x + 5y = −20 has slope −4/5, the slope of any parallel line will be the same, namely −4/5. So, to plot the parallel line, plot the point P (−1, 5), then move downwards 4 units and right 5 units, arriving at the point Q(4, 1). Draw a line through points P and Q. y 6P (−1, 5) To ﬁnd the equation of the parallel line, use the point-slope form and substitute −4/5 for m and (−1, 5) for (x0 , y0 ) Δy = −4 Q(4, 1) Δx = 5 −6 6 −6 x y − y0 = m(x − x0 ) 4 y − 5 = − (x − (−1)) 5 4 y − 5 = − (x + 1) 5 4x + 5y = −20 We must now put our ﬁnal answer in standard form. 4 y − 5 = − (x + 1) 5 4 4 y−5=− x− 5 5 Point-slope form. Distribute −4/5. Standard form does not allow fractional coeﬃcients. Clear the fractions by multiplying both sides by the common denominator. 4 4 5 5(y − 5) = − x − 5 5 Multiply both sides by 5. 5y − 25 = −4x − 4 Simplify. We need to put our result in the standard form Ax + By = C. 5y − 25 + 4x = −4x − 4 + 4x 4x + 5y − 25 = −4 4x + 5y − 25 + 25 = −4 + 25 4x + 5y = 21 Add 4x to both sides. Simplify. Add 25 to both sides. Simplify. Label the lines with their equations. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 196 y 4x + 5y = 21 6P (−1, 5) −6 6 −6 x 4x + 5y = −20 25. A sketch will help maintain our focus. First, determine the x- and yintercepts of 5x + 2y = 10. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. 5x + 2y = 10 5x + 2(0) = 10 5x + 2y = 10 5(0) + 2y = 10 5x = 10 5x 10 = 5 5 x=2 2y = 10 2y 10 = 2 2 y=5 The x-intercept is (2, 0). The y-intercept is (0, 5). Plot the x- and y-intercepts, label them with their coordinates, then draw the line through them and label the line with its equation. y 6 (0, 5) Use the intercepts (2, 0) and (0, 5) to determine the slope. Pick a direction to subtract and stay consistent. (2, 0) −6 6 −6 Second Edition: 2012-2013 x 5x + 2y = 10 Δy Δx 0−5 = 2−0 5 =− 2 m= 3.6. STANDARD FORM OF A LINE 197 Because the line 5x + 2y = 10 has slope −5/2, the slope of any perpendicular line will be its negative reciprocal, namely 2/5. So, to plot the perpendicular line, plot the point P (−1, −2), then move upwards 2 units and right 5 units, arriving at the point Q(4, 0). Draw a line through points P and Q. y 6 To ﬁnd the equation of the perpendicular line, use the point-slope form and substitute 2/5 for m and (−1, −2) for (x0 , y0 ) Δx = 5 −6 Q(4,60) Δy = 2 x P (−1, −2) −6 y − y0 = m(x − x0 ) 2 y − (−2) = (x − (−1)) 5 2 y + 2 = (x + 1) 5 5x + 2y = 10 We must now put our ﬁnal answer in standard form. 2 (x + 1) 5 2 2 y+2= x+ 5 5 y+2= Point-slope form. Distribute 2/5. Standard form does not allow fractional coeﬃcients. Clear the fractions by multiplying both sides by the common denominator. 2 2 5(y + 2) = x+ 5 Multiply both sides by 5. 5 5 5y + 10 = 2x + 2 Simplify. We need to put our result in the standard form Ax + By = C. 5y + 10 − 2x = 2x + 2 − 2x −2x + 5y + 10 = 2 −2x + 5y + 10 − 10 = 2 − 10 −2x + 5y = −8 Subtract 2x from both sides. Simplify. Subtract 10 from both sides. Simplify. Standard form Ax + By = C requires that A ≥ 0. −1(−2x + 5y) = (−8)(−1) 2x − 5y = 8 Multiply both sides by −1. Distribute −1 and simplify. Label the lines with their equations. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 198 y 6 −6 6 x P (−1, −2) 2x − 5y = 8 −6 5x + 2y = 10 27. A sketch will help maintain our focus. First, determine the x- and yintercepts of 4x + 3y = −12. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. 4x + 3y = −12 4x + 3(0) = −12 4x + 3y = −12 4(0) + 3y = −12 4x = −12 4x −12 = 4 4 x = −3 3y = −12 3y −12 = 3 3 y = −4 The x-intercept is (−3, 0). The y-intercept is (0, −4). Plot the x- and y-intercepts, label them with their coordinates, then draw the line through them and label the line with its equation. y 6 Use the intercepts (−3, 0) and (0, −4) to determine the slope. Pick a direction to subtract and stay consistent. (−3, 0) −6 6 x (0, −4) −6 4x + 3y = −12 Second Edition: 2012-2013 Δy Δx 0 − (−4) = −3 − 0 4 =− 3 m= 3.6. STANDARD FORM OF A LINE 199 Because the line 4x + 3y = −12 has slope −4/3, the slope of any perpendicular line will be its negative reciprocal, namely 3/4. So, to plot the perpendicular line, plot the point P (−4, −5), then move upwards 3 units and right 4 units, arriving at the point Q(0, −2). Draw a line through points P and Q. y 6 To ﬁnd the equation of the perpendicular line, use the point-slope form and substitute 3/4 for m and (−4, −5) for (x0 , y0 ) −6 6 Δx = 4 x Q(0, −2) Δy = 3 P (−4,−6 −5) y − y0 = m(x − x0 ) 3 y − (−5) = (x − (−4)) 4 3 y + 5 = (x + 4) 4 4x + 3y = −12 We must now put our ﬁnal answer in standard form. 3 (x + 4) 4 3 y+5= x+3 4 y+5= Point-slope form. Distribute 3/4. Standard form does not allow fractional coeﬃcients. Clear the fractions by multiplying both sides by the common denominator. 3 4(y + 5) = x+3 4 Multiply both sides by 4. 4 4y + 20 = 3x + 12 Simplify. We need to put our result in the standard form Ax + By = C. 4y + 20 − 3x = 3x + 12 − 3x −3x + 4y + 20 = 12 −3x + 4y + 20 − 20 = 12 − 20 −3x + 4y = −8 Subtract 3x from both sides. Simplify. Subtract 20 from both sides. Simplify. Standard form Ax + By = C requires that A ≥ 0. −1(−3x + 4y) = (−8)(−1) 3x − 4y = 8 Multiply both sides by −1. Distribute −1 and simplify. Label the lines with their equations. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 200 y 6 −6 3x − 4y = 8 6 P (−4,−6 −5) x 4x + 3y = −12 29. A sketch will help maintain our focus. First, determine the x- and yintercepts of 5x + 4y = 20. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. 5x + 4y = 20 5x + 4(0) = 20 5x + 4y = 20 5(0) + 4y = 20 5x = 20 5x 20 = 5 5 x=4 4y = 20 4y 20 = 4 4 y=5 The x-intercept is (4, 0). The y-intercept is (0, 5). Plot the x- and y-intercepts, label them with their coordinates, then draw the line through them and label the line with its equation. y 6 (0, 5) Use the intercepts (4, 0) and (0, 5) to determine the slope. Pick a direction to subtract and stay consistent. (4, 0) −6 6 x 5x + 4y = 20 −6 Second Edition: 2012-2013 Δy Δx 0−5 = 4−0 5 =− 4 m= 3.6. STANDARD FORM OF A LINE 201 Because the line 5x + 4y = 20 has slope −5/4, the slope of any parallel line will be the same, namely −5/4. So, to plot the parallel line, plot the point P (−3, 2), then move downwards 5 units and right 4 units, arriving at the point Q(1, −3). Draw a line through points P and Q. y 6 To ﬁnd the equation of the parallel line, use the point-slope form and substitute −5/4 for m and (−3, 2) for (x0 , y0 ) P (−3, 2) Δy −6 = −5 6 Δx = 4 x Q(1, −3) 5x + 4y = 20 y − y0 = m(x − x0 ) 5 y − 2 = − (x − (−3)) 4 5 y − 2 = − (x + 3) 4 −6 We must now put our ﬁnal answer in standard form. 5 y − 2 = − (x + 3) 4 5 15 y−2=− x− 4 4 Point-slope form. Distribute −5/4. Standard form does not allow fractional coeﬃcients. Clear the fractions by multiplying both sides by the common denominator. 4(y − 2) = 5 15 − x− 4 4 4 4y − 8 = −5x − 15 Multiply both sides by 4. Simplify. We need to put our result in the standard form Ax + By = C. 4y − 8 + 5x = −5x − 15 + 5x 5x + 4y − 8 = −15 5x + 4y − 8 + 8 = −15 + 8 5x + 4y = −7 Add 5x to both sides. Simplify. Add 8 to both sides. Simplify. Label the lines with their equations. Second Edition: 2012-2013 CHAPTER 3. INTRODUCTION TO GRAPHING 202 y 5x + 4y = −7 6 P (−3, 2) −6 6 x 5x + 4y = 20 −6 31. Plot the point P (−5, −4) and draw a horizontal line through the point. y 6 −6 6 x (−5, −4) y = −4 −6 Because every point on the line has a y-value equal to −4, the equation of the line is y = −4. 33. Plot the point P (−2, −4) and draw a vertical line through the point. Second Edition: 2012-2013 3.6. STANDARD FORM OF A LINE 203 y x = −2 6 −6 6 x (−2, −4) −6 Because every point on the line has a x-value equal to −2, the equation of the line is x = −2. Second Edition: 2012-2013 Chapter 4 Systems 4.1 Solving Systems by Graphing 1. First, determine the x- and y-intercepts of 3x − 4y = 24. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. 3x − 4y = 24 3x − 4y = 24 3x − 4(0) = 24 3(0) − 4y = 24 3x = 24 x=8 −4y = 24 y = −6 Plot and label the intercepts, then draw the line 3x − 4y = 24 through them and label it with its equation. Next, the line y = − 12 x − 1 has slope −1/2 and y-intercept (0, −1). Plot and label (0, −1), then move 2 units to the right and 1 unit down. Label the resulting line with its equation. y y 3x − 4y = 24 2 (8, 0) −2 10 x 2 Δx = 2 −2 (0, −1) 10 x Δy = −1 (0, −6) y = − 21 x − 1 −10 −10 205 CHAPTER 4. SYSTEMS 206 Next, place both lines on the same coordinate system, label each line with its equation, then label the point of intersection with its coordinates. y 3x − 4y = 24 2 −2 10 x (4, −3) y = − 12 x − 1 −10 Substitute the point (x, y) = (4, −3) in both equations to see if it checks. 1 y =− x−1 2 1 −3 = − (4) − 1 2 −3 = −3 3x − 4y = 24 3(4) − 4(−3) = 24 24 = 24 Hence, the solution (x, y) = (4, −3) checks. 3. First, determine the x- and y-intercepts of 2x + y = 6. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. 2x + y = 6 2x + (0) = 6 2x + y = 6 2(0) + y = 6 2x = 6 x=3 y=6 Plot and label the intercepts, then draw the line 2x + y = 6 through them and label it with its equation. Next, the line y = x + 3 has slope 1 and yintercept (0, 3). Plot and label (0, 3), then move 1 unit to the right and 1 unit up. Label the resulting line with its equation. Second Edition: 2012-2013 4.1. SOLVING SYSTEMS BY GRAPHING 207 y y 10 y = x+3 10 (0, 6) (0, 3) Δy = 1 Δx = 1 (3, 0) −2 10 −2 x −2 10 −2 2x + y = 6 Next, place both lines on the same coordinate system, label each line with its equation, then label the point of intersection with its coordinates. y y =x+3 10 (1, 4) −2 10 −2 x 2x + y = 6 Substitute the point (x, y) = (1, 4) in both equations to see if it checks. 2x + y = 6 2(1) + (4) = 6 6=6 y =x+3 4 = (1) + 3 4=4 Hence, the solution (x, y) = (1, 4) checks. Second Edition: 2012-2013 x CHAPTER 4. SYSTEMS 208 5. First, determine the x- and y-intercepts of x + 2y = −6. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. x + 2y = −6 x + 2y = −6 x + 2(0) = −6 x = −6 (0) + 2y = −6 2y = −6 y = −3 Plot and label the intercepts, then draw the line x + 2y = −6 through them and label it with its equation. Next, the line y = −3x − 8 has slope −3 and y-intercept (0, −8). Plot and label (0, −8), then move 1 unit to the left and 3 units up. Label the resulting line with its equation. y y = −3x − 8 2 (−6, 0) −10 2 x y 2 −10 2 (0, −3) x + 2y = −6 Δy = 3 (0, −8) Δx = −1 −10 −10 Next, place both lines on the same coordinate system, label each line with its equation, then label the point of intersection with its coordinates. y = −3x − 8 y 2 −10 2 x (−2, −2) x + 2y = −6 −10 Second Edition: 2012-2013 x 4.1. SOLVING SYSTEMS BY GRAPHING 209 Substitute the point (x, y) = (−2, −2) in both equations to see if it checks. x + 2y = −6 y = −3x − 8 (−2) + 2(−2) = −6 −6 = −6 −2 = −3(−2) − 8 −2 = −2 Hence, the solution (x, y) = (−2, −2) checks. 7. First, determine the x- and y-intercepts of −x − 3y = 3. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. −x − 3y = 3 −x − 3(0) = 3 −x − 3y = 3 −(0) − 3y = 3 −x = 3 −3y = 3 x = −3 y = −1 Plot and label the intercepts, then draw the line −x − 3y = 3 through them and label it with its equation. y 5 (−3, 0) (0, −1) −5 5 x −x − 3y = 3 −5 Secondly, determine the x- and y-intercepts of x − 4y = −4. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. x − 4y = −4 x − 4(0) = −4 x − 4y = −4 (0) − 4y = −4 x = −4 −4y = −4 y=1 Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 210 Plot and label the intercepts, then draw the line x − 4y = −4 through them and label it with its equation. y 5 x − 4y = −4 (0, 1) (−4, 0) −5 x 5 −5 Finally, plot both lines on the same coordinate system, label each with its equation, then label the point of intersection with its approximate coordinates. y 5 x − 4y = −4 −5 (−3.4, 0.1) 5 x −x − 3y = 3 −5 Hence, the solution is approximately (x, y) ≈ (−3.4, 0.1). Check: Remember, our estimate is an approximation so we don’t expect the solution to check exactly (though sometimes it might). Substitute the approximation (x, y) ≈ (−3.4, 0.1) in both equations to see how close it checks. We use a calculator to perform the arithmetic. −x − 3y = 3 −(−3.4) − 3(0.1) ≈ 3 x − 4y = −4 (−3.4) − 4(0.1) ≈ −4 3.1 ≈ 3 −3.8 ≈ −4 That’s fairly close, suggesting the approximation (x, y) ≈ (−3.4, 0.1) is fairly close to the proper solution. Second Edition: 2012-2013 4.1. SOLVING SYSTEMS BY GRAPHING 211 9. First, determine the x- and y-intercepts of −3x + 3y = −9. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. −3x + 3y = −9 −3x + 3(0) = −9 −3x + 3y = −9 −3(0) + 3y = −9 −3x = −9 x=3 3y = −9 y = −3 Plot and label the intercepts, then draw the line −3x + 3y = −9 through them and label it with its equation. y 5 −3x + 3y = −9 (3, 0) −5 5 x (0, −3) −5 Secondly, determine the x- and y-intercepts of −3x + 3y = −12. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. −3x + 3y = −12 −3x + 3(0) = −12 −3x + 3y = −12 −3(0) + 3y = −12 −3x = −12 x=4 3y = −12 y = −4 Plot and label the intercepts, then draw the line −3x + 3y = −12 through them and label it with its equation. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 212 y 5 (4, 0) −5 x 5 (0, −4) −5 −3x + 3y = −12 Finally, plot both lines on the same coordinate system and label each with its equation. y 5 −3x + 3y = −9 −5 5 x −5 −3x + 3y = −12 It appears that the lines might be parallel. Let’s put each into slopeintercept form to check this supposition. Solve −3x + 3y = −9 for y: Solve −3x + 3y = −12 for y: −3x + 3y = −9 −3x + 3y = −12 −3x + 3y + 3x = −9 + 3x 3y = −9 + 3x 3y −9 + 3x = 3 3 y =x−3 −3x + 3y + 3x = −12 + 3x 3y = −12 + 3x 3y −12 + 3x = 3 3 y =x−4 Note that both lines have slope 1. However, the ﬁrst line has a y-intercept at (0, −3), while the second line has a y-intercept at (0, −4). Hence, the lines are distinct and parallel. Therefore, the system has no solutions. Second Edition: 2012-2013 4.1. SOLVING SYSTEMS BY GRAPHING 213 11. First, determine the x- and y-intercepts of 6x − 7y = −42. To ﬁnd the y-intercept, let x = 0. To ﬁnd the x-intercept, let y = 0. 6x − 7y = −42 6x − 7y = −42 6x − 7(0) = −42 6x = −42 6(0) − 7y = −42 −7y = −42 x = −7 y=6 Plot and label the intercepts, then draw the line 6x − 7y = −42 through them and label it with its equation. Next, the line y = − 41 x + 4 has slope −1/4 and y-intercept (0, 4). Plot and label (0, 4), then move 4 units to the left and 1 unit up. Label the resulting line with its equation. y y 10 10 6x − 7y = −42 (0, 6) (0, 4) Δy = 1 Δx = −4 y = − 41 x + 4 (−7, 0) −10 2 x −10 2 −2 −2 Next, place both lines on the same coordinate system, label each line with its equation, then label the point of intersection with its coordinates. y 10 6x − 7y = −42 (−1.8, 4.5) y = − 14 x + 4 −10 2 x −2 Second Edition: 2012-2013 x CHAPTER 4. SYSTEMS 214 Hence, the solution is approximately (x, y) ≈ (−1.8, 4.5). Check: Remember, our estimate is an approximation so we don’t expect the solution to check exactly (though sometimes it might). Substitute the approximation (x, y) ≈ (−1.8, 4.5) in both equations to see how close it checks. We use a calculator to perform the arithmetic. 1 y =− x+4 4 1 4.5 ≈ − (−1.8) + 4 4 4.5 ≈ 4.45 6x − 7y = −42 6(−1.8) − 7(4.5) ≈ −42 −42.3 ≈ −42 That’s fairly close, suggesting the approximation (x, y) ≈ (−1.8, 4.5) is fairly close to the proper solution. 13. First, determine the x- and y-intercepts of 6x − 7y = −42. To ﬁnd the y-intercept, let x = 0. To ﬁnd the x-intercept, let y = 0. 6x − 7y = −42 6x − 7y = −42 6x − 7(0) = −42 6x = −42 6(0) − 7y = −42 −7y = −42 x = −7 y=6 Plot and label the intercepts, then draw the line 6x − 7y = −42 through them and label it with its equation. Next, the line y = − 51 x + 2 has slope −1/5 and y-intercept (0, 2). Plot and label (0, 2), then move 5 units to the left and 1 unit up. Label the resulting line with its equation. y y 10 10 6x − 7y = −42 (0, 6) (0, 2) Δy = 1 Δx = −5 (−7, 0) −10 2 −2 Second Edition: 2012-2013 x y = − 15 x + 2 x 2 −10 −2 4.1. SOLVING SYSTEMS BY GRAPHING 215 Next, place both lines on the same coordinate system, label each line with its equation, then label the point of intersection with its coordinates. y 10 6x − 7y = −42 (−3.8, 2.8) y = − 15 x + 2 x 2 −10 −2 Hence, the solution is approximately (x, y) ≈ (−3.8, 2.8). Check: Remember, our estimate is an approximation so we don’t expect the solution to check exactly (though sometimes it might). Substitute the approximation (x, y) ≈ (−3.8, 2.8) in both equations to see how close it checks. We use a calculator to perform the arithmetic. 6x − 7y = −42 6(−3.8) − 7(2.8) ≈ −42 −42.4 ≈ −42 1 y = − x+2 5 1 2.8 ≈ − (−3.8) + 2 5 2.8 ≈ 2.76 That’s fairly close, suggesting the approximation (x, y) ≈ (−3.8, 2.8) is fairly close to the proper solution. 15. First, determine the x- and y-intercepts of 6x + 3y = 12. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. 6x + 3y = 12 6x + 3y = 12 6x + 3(0) = 12 6x = 12 6(0) + 3y = 12 3y = 12 x=2 y=4 Plot and label the intercepts, then draw the line 6x + 3y = 12 through them and label it with its equation. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 216 y 5 (0, 4) (2, 0) −5 x 5 −5 6x + 3y = 12 Secondly, determine the x- and y-intercepts of −2x − y = 4. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. −2x − y = 4 −2x − y = 4 −2x − (0) = 4 −2x = 4 −2(0) − y = 4 −y = 4 x = −2 y = −4 Plot and label the intercepts, then draw the line −2x − y = 4 through them and label it with its equation. y −2x − y = 4 5 (−2, 0) −5 5 x (0, −4) −5 Finally, plot both lines on the same coordinate system and label each with its equation. Second Edition: 2012-2013 4.1. SOLVING SYSTEMS BY GRAPHING 217 y −2x − y = 4 5 −5 5 −5 x 6x + 3y = 12 It appears that the lines might be parallel. Let’s put each into slopeintercept form to check this supposition. Solve 6x + 3y = 12 for y: 6x + 3y = 12 6x + 3y − 6x = 12 − 6x 3y = 12 − 6x 12 − 6x 3y = 3 3 y = −2x + 4 Solve −2x − y = 4 for y: −2x − y = 4 −2x − y + 2x = 4 + 2x −y = 4 + 2x −y 4 + 2x = −1 −1 y = −2x − 4 Note that both lines have slope −2. However, the ﬁrst line has a y-intercept at (0, 4), while the second line has a y-intercept at (0, −4). Hence, the lines are distinct and parallel. Therefore, the system has no solutions. 17. First, determine the x- and y-intercepts of 3x + y = 3. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. 3x + y = 3 3x + (0) = 3 3x + y = 3 3(0) + y = 3 3x = 3 x=1 y=3 Plot and label the intercepts, then draw the line 3x + y = 3 through them and label it with its equation. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 218 y 5 (0, 3) (1, 0) −5 x 5 −5 3x + y = 3 Secondly, determine the x- and y-intercepts of −2x + 3y = −6. To ﬁnd the x-intercept, let y = 0. To ﬁnd the y-intercept, let x = 0. −2x + 3y = −6 −2x + 3y = −6 −2x + 3(0) = −6 −2x = −6 −2(0) + 3y = −6 3y = −6 y = −2 x=3 Plot and label the intercepts, then draw the line −2x + 3y = −6 through them and label it with its equation. y 5 −2x + 3y = −6 (3, 0) −5 (0, −2) 5 x −5 Finally, plot both lines on the same coordinate system, label each with its equation, then label the point of intersection with its approximate coordinates. Second Edition: 2012-2013 4.1. SOLVING SYSTEMS BY GRAPHING 219 y 5 −2x + 3y = −6 −5 5 (1.4, −1.1) −5 x 3x + y = 3 Hence, the solution is approximately (x, y) ≈ (1.4, −1.1). Check: Remember, our estimate is an approximation so we don’t expect the solution to check exactly (though sometimes it might). Substitute the approximation (x, y) ≈ (1.4, −1.1) in both equations to see how close it checks. We use a calculator to perform the arithmetic. 3x + y = 3 −2x + 3y = −6 3(1.4) + (−1.1) ≈ 3 3.1 ≈ 3 −2(1.4) + 3(−1.1) ≈ −6 −6.1 ≈ −6 That’s fairly close, suggesting the approximation (x, y) ≈ (1.4, −1.1) is fairly close to the proper solution. 19. Enter the equations y = 34 x + 7 and y = − 13 x + 2 in the Y= menu as shown in the ﬁrst image below. Select 6:ZStandard from the ZOOM menu to sketch the system. Press 2ND CALC to open the Calculate menu (see the second image below), then select 5:intersect. Press ENTER for “First curve,” ENTER for “Second curve,” and ENTER for “Guess.” The result is shown in the third image below. The calculator reports the solution: (x, y) ≈ (−4.615385, 3.5384615) Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 220 Rounding to the nearest tenth, we get (x, y) ≈ (−4.6, 3.5). Using the Calculator Submission Guidelines, report the solution on your homework paper as follows. y 10 y = 34 x + 7 y = − 13 x + 2 (−4.6, 3.5) −10 10 x −10 21. Enter the equations y = 43 x − 3 and y = − 74 x − 1 in the Y= menu as shown in the ﬁrst image below. Select 6:ZStandard from the ZOOM menu to sketch the system. Press 2ND CALC to open the Calculate menu (see the second image below), then select 5:intersect. Press ENTER for “First curve,” ENTER for “Second curve,” and ENTER for “Guess.” The result is shown in the third image below. The calculator reports the solution: (x, y) ≈ (1.05, −1.6) Rounding to the nearest tenth, we get (x, y) ≈ (1.1, −1.6). Using the Calculator Submission Guidelines, report the solution on your homework paper as follows. Second Edition: 2012-2013 4.1. SOLVING SYSTEMS BY GRAPHING 221 y y = 43 x − 3 10 y = − 47 x − 1 −10 (1.1, −1.6) 10 x −10 23. Enter the equations y = 16 x + 1 and y = − 37 x + 5 in the Y= menu as shown in the ﬁrst image below. Select 6:ZStandard from the ZOOM menu to sketch the system. Press 2ND CALC to open the Calculate menu (see the second image below), then select 5:intersect. Press ENTER for “First curve,” ENTER for “Second curve,” and ENTER for “Guess.” The result is shown in the third image below. The calculator reports the solution: (x, y) ≈ (6.72, 2.12) Rounding to the nearest tenth, we get (x, y) ≈ (6.7, 2.1). Using the Calculator Submission Guidelines, report the solution on your homework paper as follows. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 222 y y= − 37 x 10 +5 y = 16 x + 1 (6.7, 2.1) −10 10 x −10 25. First, solve each equation for y, so that we can enter the resulting equations into the Y= menu. 6x + 16y = 96 6x + 16y − 6x = 96 − 6x −6x + 13y = −78 −6x + 13y + 6x = −78 + 6x 16y = 96 − 6x 13y = −78 + 6x 96 − 6x −78 + 6x 16y 13y = = 16 16 13 13 3 6 y =6− x y = −6 + x 8 13 6 Enter the equations y = 6− 38 x and y = −6+ 13 x in the Y= menu as shown in the ﬁrst image below. Select 6:ZStandard from the ZOOM menu to sketch the system. Make the adjustments in the second image shown below so that the point of intersection of the two lines is visible in the viewing window. Press 2ND CALC to open the Calculate menu, then select 5:intersect. Press ENTER for “First curve,” ENTER for “Second curve,” and ENTER for “Guess.” The result is shown in the third image below. The calculator reports the solution: (x, y) ≈ (14.344828, 0.62068966) Second Edition: 2012-2013 4.1. SOLVING SYSTEMS BY GRAPHING 223 Rounding to the nearest tenth, we get (x, y) ≈ (14.3, 0.6). Using the Calculator Submission Guidelines, report the solution on your homework paper as follows. y 10 6x + 16y = 96 (14.3, 0.6) −5 20 x −6x + 13y = −78 −10 27. First, solve each equation for y, so that we can enter the resulting equations into the Y= menu. −2x − 11y = 22 −2x − 11y + 2x = 22 + 2x −11y = 22 + 2x −11y 22 + 2x = −11 −11 2 y = −2 − x 11 8x − 12y = −96 8x − 12y − 8x = −96 − 8x −12y = −96 − 8x −96 − 8x −12y = −12 −12 2 y =8+ x 3 2 x and y = 8+ 23 x in the Y= menu as shown Enter the equations y = −2− 11 in the ﬁrst image below. Select 6:ZStandard from the ZOOM menu to sketch the system. Make the adjustments in the second image shown below so that the point of intersection of the two lines is visible in the viewing window. Press 2ND CALC to open the Calculate menu, then select 5:intersect. Press ENTER for “First curve,” ENTER for “Second curve,” and ENTER for “Guess.” The result is shown in the third image below. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 224 The calculator reports the solution: (x, y) ≈ (−11.78571, 0.14285714) Rounding to the nearest tenth, we get (x, y) ≈ (−11.8, 0.1). Using the Calculator Submission Guidelines, report the solution on your homework paper as follows. y 10 −20 8x − 12y = −96 (−11.8, 0.1) 5 x −2x − 11y = 22 −10 29. First, solve each equation for y, so that we can enter the resulting equations into the Y= menu. −6x + 2y = −12 −12x + 3y = −36 −6x + 2y + 6x = −12 + 6x 2y = −12 + 6x −12 + 6x 2y = 2 2 y = −6 + 3x −12x + 3y + 12x = −36 + 12x 3y = −36 + 12x 3y −36 + 12x = 3 3 y = −12 + 4x Enter the equations y = −6+3x and y = −12+4x in the Y= menu as shown in the ﬁrst image below. Select 6:ZStandard from the ZOOM menu to sketch the system. Make the adjustments in the second image shown below so that Second Edition: 2012-2013 4.1. SOLVING SYSTEMS BY GRAPHING 225 the point of intersection of the two lines is visible in the viewing window. Press 2ND CALC to open the Calculate menu, then select 5:intersect. Press ENTER for “First curve,” ENTER for “Second curve,” and ENTER for “Guess.” The result is shown in the third image below. The calculator reports the solution: (x, y) ≈ (6, 12) Rounding to the nearest tenth, we get (x, y) ≈ (6.0, 12.0). Using the Calculator Submission Guidelines, report the solution on your homework paper as follows. y −6x + 2y = −12 20 (6.0, 12.0) −10 10 x −12x + 3y = −5−36 Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 226 4.2 Solving Systems by Substitution 1. The second equation, y = 6 − 2x, is already solved for y. Substitute 6 − 2x for y in the ﬁrst equation and solve for x. −7x + 7y = 63 −7x + 7(6 − 2x) = 63 −7x + 42 − 14x = 63 42 − 21x = 63 −21x = 21 x = −1 First Equation. Substitute 6 − 2x for y. Distribute the 7. Combine like terms. Subtract 42 from both sides. Divide both sides by −21. Finally, to ﬁnd the y-value, substitute −1 for x in the equation y = 6 − 2x. y = 6 − 2x y = 6 − 2(−1) y =6+2 Substitute −1 for x. Multiply. y=8 Simplify. Hence, (x, y) = (−1, 8) is the solution of the system. Check: We now show that the solution satisﬁes both equations. Substitute (x, y) = (−1, 8) in the ﬁrst equation. −7x + 7y = 63 −7(−1) + 7(8) = 63 7 + 56 = 63 63 = 63 Substitute (x, y) = (−1, 8) in the second equation. y = 6 − 2x 8 = 6 − 2(−1) 8=6+2 8=8 The last statement in each check, being a true statement, shows that the solution (x, y) = (−1, 8) satisﬁes both equations and thus is a solution of the system. 3. The ﬁrst equation, x = 19 + 7y, is already solved for x. Substitute 19 + 7y for x in the second equation and solve for y. 3x − 3y = 3 3(19 + 7y) − 3y = 3 57 + 21y − 3y = 3 57 + 18y = 3 18y = −54 y = −3 Second Edition: 2012-2013 Second Equation. Substitute 19 + 7y for x. Distribute the 3. Combine like terms. Subtract 57 from both sides. Divide both sides by 18. 4.2. SOLVING SYSTEMS BY SUBSTITUTION 227 Finally, to ﬁnd the x-value, substitute −3 for y in the equation x = 19 + 7y. x = 19 + 7y x = 19 + 7(−3) x = 19 − 21 Substitute −3 for y. Multiply. x = −2 Simplify. Hence, (x, y) = (−2, −3) is the solution of the system. Check: We now show that the solution satisﬁes both equations. Substitute (x, y) = (−2, −3) in the ﬁrst equation. Substitute (x, y) = (−2, −3) in the second equation. 3x − 3y = 3 x = 19 + 7y −2 = 19 + 7(−3) −2 = 19 − 21 3(−2) − 3(−3) = 3 −6 + 9 = 3 −2 = −2 3=3 The last statement in each check, being a true statement, shows that the solution (x, y) = (−2, −3) satisﬁes both equations and thus is a solution of the system. 5. The ﬁrst equation, x = −5 − 2y, is already solved for x. Substitute −5 − 2y for x in the second equation and solve for y. −2x − 6y = 18 −2(−5 − 2y) − 6y = 18 10 + 4y − 6y = 18 10 − 2y = 18 −2y = 8 y = −4 Second Equation. Substitute −5 − 2y for x. Distribute the −2. Combine like terms. Subtract 10 from both sides. Divide both sides by −2. Finally, to ﬁnd the x-value, substitute −4 for y in the equation x = −5 − 2y. x = −5 − 2y x = −5 − 2(−4) x = −5 + 8 Substitute −4 for y. Multiply. x=3 Simplify. Hence, (x, y) = (3, −4) is the solution of the system. Check: We now show that the solution satisﬁes both equations. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 228 Substitute (x, y) = (3, −4) in the ﬁrst equation. Substitute (x, y) = (3, −4) in the second equation. x = −5 − 2y 3 = −5 − 2(−4) −2x − 6y = 18 −2(3) − 6(−4) = 18 3 = −5 + 8 3=3 −6 + 24 = 18 18 = 18 The last statement in each check, being a true statement, shows that the solution (x, y) = (3, −4) satisﬁes both equations and thus is a solution of the system. 7. The second equation, y = 15 + 3x, is already solved for y. Substitute 15 + 3x for y in the ﬁrst equation and solve for x. 6x − 8y = 24 6x − 8(15 + 3x) = 24 First Equation. Substitute 15 + 3x for y. 6x − 120 − 24x = 24 −120 − 18x = 24 Distribute the −8. Combine like terms. −18x = 144 x = −8 Add 120 to both sides. Divide both sides by −18. Finally, to ﬁnd the y-value, substitute −8 for x in the equation y = 15 + 3x. y = 15 + 3x y = 15 + 3(−8) y = 15 − 24 Substitute −8 for x. Multiply. y = −9 Simplify. Hence, (x, y) = (−8, −9) is the solution of the system. Check: We now show that the solution satisﬁes both equations. Substitute (x, y) = (−8, −9) in the ﬁrst equation. Substitute (x, y) = (−8, −9) in the second equation. 6x − 8y = 24 6(−8) − 8(−9) = 24 y = 15 + 3x −9 = 15 + 3(−8) −48 + 72 = 24 24 = 24 −9 = 15 − 24 −9 = −9 The last statement in each check, being a true statement, shows that the solution (x, y) = (−8, −9) satisﬁes both equations and thus is a solution of the system. Second Edition: 2012-2013 4.2. SOLVING SYSTEMS BY SUBSTITUTION 229 9. The ﬁrst step is to solve either equation for either variable. This means that we could solve the ﬁrst equation for x or y, but it also means that we could solve the second equation for x or y. Of these four possible choices, solving the ﬁrst equation for x seems the easiest way to start. −x + 9y = 46 First Equation. −x = 46 − 9y x = −46 + 9y Subtract 9y from both sides. Multiply both sides by −1. Next, substitute −46 + 9y for x in the second equation and solve for x. 7x − 4y = −27 7(−46 + 9y) − 4y = −27 −322 + 63y − 4y = −27 −322 + 59y = −27 59y = 295 y=5 Second Equation. Substitute −46 + 9y for x. Distribute the 7. Combine like terms. Add 322 to both sides. Divide both sides by 59. Finally, to ﬁnd the x-value, substitute 5 for y in the equation x = −46 + 9y. x = −46 + 9y x = −46 + 9(5) Substitute 5 for y. x = −46 + 45 x = −1 Multiply. Simplify. Hence, (x, y) = (−1, 5) is the solution of the system. 11. The ﬁrst step is to solve either equation for either variable. This means that we could solve the ﬁrst equation for x or y, but it also means that we could solve the second equation for x or y. Of these four possible choices, solving the ﬁrst equation for x seems the easiest way to start. −x + 4y = 22 −x = 22 − 4y x = −22 + 4y First Equation. Subtract 4y from both sides. Multiply both sides by −1. Next, substitute −22 + 4y for x in the second equation and solve for x. 8x + 7y = −20 8(−22 + 4y) + 7y = −20 Second Equation. Substitute −22 + 4y for x. −176 + 32y + 7y = −20 Distribute the 8. −176 + 39y = −20 39y = 156 y=4 Combine like terms. Add 176 to both sides. Divide both sides by 39. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 230 Finally, to ﬁnd the x-value, substitute 4 for y in the equation x = −22 + 4y. x = −22 + 4y x = −22 + 4(4) Substitute 4 for y. x = −22 + 16 x = −6 Multiply. Simplify. Hence, (x, y) = (−6, 4) is the solution of the system. 13. The ﬁrst step is to solve either equation for either variable. This means that we could solve the ﬁrst equation for x or y, but it also means that we could solve the second equation for x or y. Of these four possible choices, solving the ﬁrst equation for x seems the easiest way to start. x + 2y = −4 x = −4 − 2y First Equation. Subtract 2y from both sides. Next, substitute −4 − 2y for x in the second equation and solve for y. 6x − 4y = −56 6(−4 − 2y) − 4y = −56 Second Equation. Substitute −4 − 2y for x. −24 − 12y − 4y = −56 −24 − 16y = −56 Distribute the 6. Combine like terms. −16y = −32 y=2 Add 24 to both sides. Divide both sides by −16. Finally, to ﬁnd the x-value, substitute 2 for y in the equation x = −4 − 2y. x = −4 − 2y x = −4 − 2(2) Substitute 2 for y. x = −4 − 4 x = −8 Multiply. Simplify. Hence, (x, y) = (−8, 2) is the solution of the system. 15. The ﬁrst step is to solve either equation for either variable. This means that we could solve the ﬁrst equation for x or y, but it also means that we could solve the second equation for x or y. Of these four possible choices, solving the ﬁrst equation for x seems the easiest way to start. x + 6y = −49 x = −49 − 6y Second Edition: 2012-2013 First Equation. Subtract 6y from both sides. 4.2. SOLVING SYSTEMS BY SUBSTITUTION 231 Next, substitute −49 − 6y for x in the second equation and solve for y. −3x + 4y = −7 −3(−49 − 6y) + 4y = −7 147 + 18y + 4y = −7 147 + 22y = −7 22y = −154 y = −7 Second Equation. Substitute −49 − 6y for x. Distribute the −3. Combine like terms. Subtract 147 from both sides. Divide both sides by 22. Finally, to ﬁnd the x-value, substitute −7 for y in the equation x = −49 − 6y. x = −49 − 6y x = −49 − 6(−7) x = −49 + 42 Substitute −7 for y. Multiply. x = −7 Simplify. Hence, (x, y) = (−7, −7) is the solution of the system. 17. 19. The ﬁrst equation, x = −2y − 4, is already solved for x, so let’s substitute −2y − 4 for x in the second equation. −4x − 8y = −6 −4 (−2y − 4) − 8y = −6 8y + 16 − 8y = −6 16 = −6 Second Equation. Substitute −2y − 4 for x. Distribute the −4. Combine like terms. The resulting statement, 16 = −6, is false. This should give us a clue that there are no solutions. Perhaps we are dealing with parallel lines? Let’s put both equations in slope-intercept form so that we can compare them. Solve x = −2y − 4 for y: x = −2y − 4 x + 4 = −2y x+4 =y −2 1 y =− x−2 2 Solve −4x − 8y = −6 for y: −4x − 8y = −6 −8y = 4x − 6 4x − 6 y= −8 1 3 y = − x+ 2 4 Hence, the lines have the same slope, −1/2, but diﬀerent y-intercepts (one has y-intercept (0, −2), the other has y-intercept (0, 3/4). Hence, these are two distinct parallel lines and the system has no solution. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 232 21. The ﬁrst step is to solve either equation for either variable. This means that we could solve the ﬁrst equation for x or y, but it also means that we could solve the second equation for x or y. Of these four possible choices, solving the second equation for y seems the easiest way to start. −7x + y = 19 y = 19 + 7x Second Equation. Add 7x to both sides. Next, substitute 19 + 7x for y in the ﬁrst equation and solve for x. −2x − 2y = 26 −2x − 2(19 + 7x) = 26 −2x − 38 − 14x = 26 −38 − 16x = 26 −16x = 64 x = −4 First Equation. Substitute y = 19 + 7x for y. Distribute the −2. Combine like terms. Add 38 to both sides. Divide both sides by −16. Finally, to ﬁnd the y-value, substitute −4 for x in the equation y = 19 + 7x. y = 19 + 7x y = 19 + 7(−4) y = 19 − 28 Substitute −4 for x. Multiply. y = −9 Simplify. Hence, (x, y) = (−4, −9) is the solution of the system. 23. The ﬁrst step is to solve either equation for either variable. This means that we could solve the ﬁrst equation for x or y, but it also means that we could solve the second equation for x or y. Of these four possible choices, solving the second equation for y seems the easiest way to start. −3x + y = 22 y = 22 + 3x Second Equation. Add 3x to both sides. Next, substitute 22 + 3x for y in the ﬁrst equation and solve for x. 3x − 4y = −43 3x − 4(22 + 3x) = −43 3x − 88 − 12x = −43 −88 − 9x = −43 −9x = 45 x = −5 Second Edition: 2012-2013 First Equation. Substitute y = 22 + 3x for y. Distribute the −4. Combine like terms. Add 88 to both sides. Divide both sides by −9. 4.2. SOLVING SYSTEMS BY SUBSTITUTION 233 Finally, to ﬁnd the y-value, substitute −5 for x in the equation y = 22 + 3x. y = 22 + 3x y = 22 + 3(−5) y = 22 − 15 Substitute −5 for x. Multiply. y=7 Simplify. Hence, (x, y) = (−5, 7) is the solution of the system. 25. 27. The second equation, y = − 87 x+9, is already solved for y, so let’s substitute − 87 x + 9 for y in the ﬁrst equation. −8x − 7y = 2 8 −8x − 7 − x + 9 = 2 7 −8x + 8x − 63 = 2 −63 = 2 First Equation. 8 Substitute − x + 9 for y. 7 Distribute the −7. Combine like terms. The resulting statement, −63 = 2, is false. This should give us a clue that there are no solutions. Perhaps we are dealing with parallel lines? The second equation is already solved for y so let’s solve the ﬁrst equation for y to determine the situation. −8x − 7y = 2 −7y = 8x + 2 8x + 2 y= −7 2 8 y =− x− 7 7 First Equation. Add 8x to both sides. Divide both sides by −7. Divide both terms by −7. Thus, our system is equivalent to the following system of equations. 8 2 y =− x− 7 7 8 y =− x+9 7 These lines have the same slope, −8/7, but diﬀerent y-intercepts (one has y-intercept (0, −2/7), the other has y-intercept (0, 9). Hence, these are two distinct parallel lines and the system has no solution. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 234 29. We begin by solving the ﬁrst equation for x. 3x − 5y = 3 First equation. 3x = 3 + 5y 3 + 5y x= 3 5 x=1+ y 3 Add 5y to both sides Divide both sides by 3. Divide both terms by 3. 5 Next, substitute 1 + y for x in the second equation. 3 5x − 7y 5 5 1 + y − 7y 3 25 5 + y − 7y 3 15 + 25y − 21y 15 + 4y =2 Second equation. =2 5 Substitute 1 + y for x. 3 =2 Distribute the 5. =6 =6 Multiply both sides by 3. Combine like terms. 4y = −9 9 y=− 4 Subtract 15 from both sides. Divide both sides by 4. 5 Finally, substitute −9/4 for y in x = 1 + y. 3 5 x=1+ y 3 5 9 x=1+ − 3 4 15 x=1− 4 4 15 x= − 4 4 x=− Substitute −9/4 for y. Multiply. Equivalent fractions with. a common denominator. 11 4 Simplify. Hence, (x, y) = (−11/4, −9/4) is the solution of the system. Check: First, store −11/4 in X with the following keystrokes. The result is shown in the ﬁrst image below. (-) 1 1 ÷ 4 STO X, T, θ, n ENTER Store −9/4 in Y with the following keystrokes. The result is shown in the ﬁrst image below. Second Edition: 2012-2013 4.2. SOLVING SYSTEMS BY SUBSTITUTION (-) 9 ÷ 4 STO ALPHA 235 1 ENTER Clear the calculator screen by pressing the CLEAR button, then enter the lefthand side of the ﬁrst equation with the following keystrokes. The result is shown in the second image below. 3 × X, T, θ, n − 5 × ALPHA 1 ENTER Enter the left-hand side of the second equation with the following keystrokes. The result is shown in the second image below. 5 × X, T, θ, n − 7 × ALPHA 1 ENTER The result in the second image shows that 3x − 5y = 3 and 5x − 7y = 2 for x = −11/4 and y = −9/4. The solution checks. 31. We begin by solving the ﬁrst equation for x. 4x + 3y = 8 First equation. 4x = 8 − 3y Subtract 3y from both sides 8 − 3y Divide both sides by 4. x= 4 3 x=2− y Divide both terms by 4. 4 3 Next, substitute 2 − y for x in the second equation. 4 3x + 4y 3 3 2 − y + 4y 4 9 6 − y + 4y 4 24 − 9y + 16y 24 + 7y =2 Second equation. =2 3 Substitute 2 − y for x. 4 =2 Distribute the 3. =8 =8 Multiply both sides by 4. Combine like terms. 7y = −16 16 y=− 7 Subtract 24 from both sides. Divide both sides by 7. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 236 3 Finally, substitute −16/7 for y in x = 2 − y. 4 3 x=2− y 4 3 16 x=2− − Substitute −16/7 for y. 4 7 12 Multiply. x=2+ 7 14 12 x= + Equivalent fractions with. 7 7 a common denominator. 26 Simplify. x= 7 Hence, (x, y) = (26/7, −16/7) is the solution of the system. Check: First, store 26/7 in X with the following keystrokes. The result is shown in the ﬁrst image below. 2 6 ÷ 7 STO X, T, θ, n ENTER Store −16/7 in Y with the following keystrokes. The result is shown in the ﬁrst image below. (-) 1 6 ÷ 7 STO ALPHA 1 ENTER Clear the calculator screen by pressing the CLEAR button, then enter the lefthand side of the ﬁrst equation with the following keystrokes. The result is shown in the second image below. 4 × X, T, θ, n + 3 × ALPHA 1 ENTER Enter the left-hand side of the second equation with the following keystrokes. The result is shown in the second image below. 3 × X, T, θ, n + 4 × ALPHA 1 ENTER The result in the second image shows that 4x + 3y = 8 and 3x + 4y = 2 for x = 26/7 and y = −16/7. The solution checks. Second Edition: 2012-2013 4.2. SOLVING SYSTEMS BY SUBSTITUTION 237 33. We begin by solving the ﬁrst equation for x. 3x + 8y = 6 First equation. 3x = 6 − 8y 6 − 8y x= 3 8 x=2− y 3 Subtract 8y from both sides Divide both sides by 3. Divide both terms by 3. 8 Next, substitute 2 − y for x in the second equation. 3 2x + 7y 8 2 2 − y + 7y 3 16 4 − y + 7y 3 12 − 16y + 21y 12 + 5y = −2 Second equation. = −2 8 Substitute 2 − y for x. 3 = −2 Distribute the 2. = −6 = −6 Multiply both sides by 3. Combine like terms. 5y = −18 18 y=− 5 Subtract 12 from both sides. Divide both sides by 5. 8 Finally, substitute −18/5 for y in x = 2 − y. 3 8 x=2− y 3 8 18 x=2− − 3 5 48 x=2+ 5 10 48 x= + 5 5 x= Substitute −18/5 for y. Multiply. Equivalent fractions with. a common denominator. 58 5 Simplify. Hence, (x, y) = (58/5, −18/5) is the solution of the system. Check: First, store 58/5 in X with the following keystrokes. The result is shown in the ﬁrst image below. 5 8 ÷ 5 STO X, T, θ, n ENTER Store −18/5 in Y with the following keystrokes. The result is shown in the ﬁrst image below. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 238 (-) 1 8 ÷ 5 STO ALPHA 1 ENTER Clear the calculator screen by pressing the CLEAR button, then enter the lefthand side of the ﬁrst equation with the following keystrokes. The result is shown in the second image below. 3 × X, T, θ, n + 8 × ALPHA 1 ENTER Enter the left-hand side of the second equation with the following keystrokes. The result is shown in the second image below. 2 × X, T, θ, n + 7 × ALPHA 1 ENTER The result in the second image shows that 3x + 8y = 6 and 2x + 7y = −2 for x = 58/5 and y = −18/5. The solution checks. 35. We begin by solving the ﬁrst equation for x. 4x + 5y = 4 First equation. 4x = 4 − 5y Subtract 5y from both sides 4 − 5y Divide both sides by 4. x= 4 5 x=1− y Divide both terms by 4. 4 5 Next, substitute 1 − y for x in the second equation. 4 −3x − 2y 5 −3 1 − y − 2y 4 15 −3 + y − 2y 4 −12 + 15y − 8y −12 + 7y =1 Second equation. =1 5 Substitute 1 − y for x. 4 =1 Distribute the −3. =4 =4 Multiply both sides by 4. Combine like terms. 7y = 16 16 y= 7 Second Edition: 2012-2013 Add 12 to both sides. Divide both sides by 7. 4.2. SOLVING SYSTEMS BY SUBSTITUTION 239 5 Finally, substitute 16/7 for y in x = 1 − y. 4 5 x=1− y 4 5 16 x=1− Substitute 16/7 for y. 4 7 20 Multiply. x=1− 7 7 20 x= − Equivalent fractions with. 7 7 a common denominator. 13 Simplify. x=− 7 Hence, (x, y) = (−13/7, 16/7) is the solution of the system. Check: First, store −13/7 in X with the following keystrokes. The result is shown in the ﬁrst image below. (-) 1 3 ÷ 7 STO X, T, θ, n ENTER Store 16/7 in Y with the following keystrokes. The result is shown in the ﬁrst image below. 1 6 ÷ 7 STO ALPHA 1 ENTER Clear the calculator screen by pressing the CLEAR button, then enter the lefthand side of the ﬁrst equation with the following keystrokes. The result is shown in the second image below. × 4 X, T, θ, n + × 5 ALPHA 1 ENTER Enter the left-hand side of the second equation with the following keystrokes. The result is shown in the second image below. (-) 3 × X, T, θ, n − 2 × ALPHA 1 ENTER The result in the second image shows that 4x + 5y = 4 and −3x − 2y = 1 for x = −13/7 and y = 16/7. The solution checks. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 240 37. The second equation, y = 32 x − 8, is already solved for y, so let’s substitute 3 2 x − 8 for y in the ﬁrst equation. −9x + 6y = 9 3 x−8 = 9 −9x + 6 2 −9x + 9x − 48 = 9 −48 = 9 First Equation. Substitute 3 x − 8 for y. 2 Distribute the 6. Combine like terms. The resulting statement, −48 = 9, is false. This should give us a clue that there are no solutions. Perhaps we are dealing with parallel lines? The second equation is already solved for y so let’s solve the ﬁrst equation for y to determine the situation. −9x + 6y = 9 6y = 9x + 9 9x + 9 y= 6 3 3 y = x+ 2 2 First Equation. Add 9x to both sides. Divide both sides by 6. Divide both terms by 6. Thus, our system is equivalent to the following system of equations. 3 3 x+ 2 2 3 y = x−8 2 y= These lines have the same slope, 3/2, but diﬀerent y-intercepts (one has yintercept (0, 3/2), the other has y-intercept (0, −8). Hence, these are two distinct parallel lines and the system has no solution. 39. The ﬁrst equation, y = −2x − 16, is already solved for y, so let’s substitute −2x − 16 for y in the second equation. −14x − 7y = 112 −14x − 7(−2x − 16) = 112 −14x + 14x + 112 = 112 112 = 112 Second Equation. Substitute −2x − 16 for y. Distribute the −7. Combine like terms. The resulting statement, 112 = 112, is a true statement. Perhaps this is an indication that we are dealing with the same line? Since the ﬁrst equation is already in slope-intercept form, let’s put the second equation into slopeSecond Edition: 2012-2013 4.2. SOLVING SYSTEMS BY SUBSTITUTION 241 intercept form so that we can compare them. −14x − 7y = 112 −7y = 14x + 112 14x + 112 y= −7 y = −2x − 16 Second Equation. Add 14x to both sides. Divide both sides by −7. Divide both terms by −7. Thus, our system is equivalent to the following system of equations. y = −2x − 16 y = −2x − 16 These two lines have the same slope and the same y-intercept and they are exactly the same lines. Thus, there are an inﬁnite number of solutions. Indeed, any point on either line is a solution. 41. The ﬁrst equation, x = 16 − 5y, is already solved for x. Substitute 16 − 5y for x in the second equation and solve for y. −4x + 2y = 24 −4(16 − 5y) + 2y = 24 −64 + 20y + 2y = 24 −64 + 22y = 24 22y = 88 y=4 Second Equation. Substitute 16 − 5y for x. Distribute the −4. Combine like terms. Add 64 to both sides. Divide both sides by 22. Finally, to ﬁnd the x-value, substitute 4 for y in the equation x = 16 − 5y. x = 16 − 5y x = 16 − 5(4) Substitute 4 for y. x = 16 − 20 x = −4 Multiply. Simplify. Hence, (x, y) = (−4, 4) is the solution of the system. 43. The ﬁrst equation, x = 7y + 18, is already solved for x, so let’s substitute 7y + 18 for x in the second equation. 9x − 63y = 162 9(7y + 18) − 63y = 162 63y + 162 − 63y = 162 162 = 162 Second Equation. Substitute 7y + 18 for x. Distribute the 9. Combine like terms. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 242 The resulting statement, 162 = 162, is a true statement. Perhaps this is an indication that we are dealing with the same line? Let’s put the ﬁrst and second equations into slope-intercept form so that we can compare them. Solve 9x − 63y = 162 for y: Solve x = 7y + 18 for y: 9x − 63y = 162 −63y = −9x + 162 −9x + 162 y= −63 18 1 y = x− 7 7 Thus, our system is equivalent to the following system of equations. x = 7y + 18 x − 18 = 7y x − 18 =y 7 1 18 y = x− 7 7 1 x− 7 1 y = x− 7 y= 18 7 18 7 These two lines have the same slope and the same y-intercept and they are exactly the same lines. Thus, there are an inﬁnite number of solutions. Indeed, any point on either line is a solution. 45. The ﬁrst equation, x = −2y + 3, is already solved for x, so let’s substitute −2y + 3 for x in the second equation. 4x + 8y = 4 4 (−2y + 3) + 8y = 4 −8y + 12 + 8y = 4 12 = 4 Second Equation. Substitute −2y + 3 for x. Distribute the 4. Combine like terms. The resulting statement, 12 = 4, is false. This should give us a clue that there are no solutions. Perhaps we are dealing with parallel lines? Let’s put both equations in slope-intercept form so that we can compare them. Solve x = −2y + 3 for y: x = −2y + 3 x − 3 = −2y x−3 =y −2 1 3 y =− x+ 2 2 Solve 4x + 8y = 4 for y: 4x + 8y = 4 8y = −4x + 4 −4x + 4 y= 8 1 1 y = − x+ 2 2 Hence, the lines have the same slope, −1/2, but diﬀerent y-intercepts (one has y-intercept (0, 3/2), the other has y-intercept (0, 1/2). Hence, these are two distinct parallel lines and the system has no solution. Second Edition: 2012-2013 4.3. SOLVING SYSTEMS BY ELIMINATION 243 47. The second equation, y = −3 − 2x, is already solved for y. Substitute −3 − 2x for y in the ﬁrst equation and solve for x. −9x + 4y = 73 −9x + 4(−3 − 2x) = 73 First Equation. Substitute −3 − 2x for y. −9x − 12 − 8x = 73 −12 − 17x = 73 Distribute the 4. Combine like terms. −17x = 85 x = −5 Add 12 to both sides. Divide both sides by −17. Finally, to ﬁnd the y-value, substitute −5 for x in the equation y = −3 − 2x. y = −3 − 2x y = −3 − 2(−5) y = −3 + 10 Substitute −5 for x. Multiply. y=7 Simplify. Hence, (x, y) = (−5, 7) is the solution of the system. 4.3 Solving Systems by Elimination 1. Start with the given system. x + 9x − 4y 7y = = 0 −43 We’ll concentrate on eliminating x. Multiply the ﬁrst equation by −9, then add the results. −9x − 36y = 0 9x − 7y = −43 − 43y = −43 Divide both sides by −43. −43 −43 y=1 y= Divide both sides by −43. Simplify. Take the answer y = 1 and substitute 1 for y in the ﬁrst equation. x + 4y = 0 x + 4(1) = 0 x+4=0 x = −4 First equation. Substitute 1 for y. Multiply. Subtract 4 from both sides. Hence, the solution is (x, y) = (−4, 1). Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 244 Check: We must show that the solution (x, y) = (−4, 1) satisﬁes both equations. x + 4y = 0 9x − 7y = −43 (−4) + 4(1) = 0 −4 + 4 = 0 9(−4) − 7(1) = −43 −36 − 7 = −43 0=0 −43 = −43 Because each of the last two statements are true, this guarantees that (x, y) = (−4, 1) is a solution of the system. 3. Start with the given system. 6x + y 4x + 2y = = 8 0 We’ll concentrate on eliminating y. Multiply the ﬁrst equation by −2, then add the results. −12x − 2y = −16 4x + 2y = 0 −8x = −16 Divide both sides by −8. −16 −8 x=2 x= Divide both sides by −8. Simplify. Take the answer x = 2 and substitute 2 for x in the ﬁrst equation. 6x + y = 8 First equation. 6(2) + y = 8 12 + y = 8 Substitute 2 for x. Multiply. y = −4 Subtract 12 from both sides. Hence, the solution is (x, y) = (2, −4). Check: We must show that the solution (x, y) = (2, −4) satisﬁes both equations. 6x + y = 8 4x + 2y = 0 6(2) + (−4) = 8 12 − 4 = 8 4(2) + 2(−4) = 0 8−8=0 8=8 0=0 Second Edition: 2012-2013 4.3. SOLVING SYSTEMS BY ELIMINATION 245 Because each of the last two statements are true, this guarantees that (x, y) = (2, −4) is a solution of the system. 5. Start with the given system. −8x + 4x + y 3y = = −56 56 We’ll concentrate on eliminating y. Multiply the ﬁrst equation by −3, then add the results. 24x − 3y = 168 4x + 3y = 56 28x = 224 Divide both sides by 28. 224 28 x=8 Divide both sides by 28. x= Simplify. Take the answer x = 8 and substitute 8 for x in the ﬁrst equation. −8x + y = −56 −8(8) + y = −56 First equation. Substitute 8 for x. −64 + y = −56 y=8 Multiply. Add 64 to both sides. Hence, the solution is (x, y) = (8, 8). Check: We must show that the solution (x, y) = (8, 8) satisﬁes both equations. −8x + y = −56 −8(8) + (8) = −56 4x + 3y = 56 4(8) + 3(8) = 56 −64 + 8 = −56 32 + 24 = 56 −56 = −56 56 = 56 Because each of the last two statements are true, this guarantees that (x, y) = (8, 8) is a solution of the system. 7. Start with the given system. x + −5x − 8y 9y = = 41 −50 Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 246 We’ll concentrate on eliminating x. Multiply the ﬁrst equation by 5, then add the results. 5x + 40y = 205 −5x − 9y = −50 31y = 155 Divide both sides by 31. 155 31 y=5 Divide both sides by 31. y= Simplify. Take the answer y = 5 and substitute 5 for y in the ﬁrst equation. x + 8y = 41 First equation. x + 8(5) = 41 x + 40 = 41 Substitute 5 for y. Multiply. x=1 Subtract 40 from both sides. Hence, the solution is (x, y) = (1, 5). Check: We must show that the solution (x, y) = (1, 5) satisﬁes both equations. x + 8y = 41 −5x − 9y = −50 (1) + 8(5) = 41 1 + 40 = 41 −5(1) − 9(5) = −50 −5 − 45 = −50 41 = 41 −50 = −50 Because each of the last two statements are true, this guarantees that (x, y) = (1, 5) is a solution of the system. 9. Start with the given system. −12x + 9y −6x − 4y = = 0 −34 We’ll concentrate on eliminating x. Multiply the second equation by −2, then add the results. −12x + 9y = 0 12x + 8y = 68 17y Second Edition: 2012-2013 = 68 4.3. SOLVING SYSTEMS BY ELIMINATION 247 Divide both sides by 17. 17y = 68 68 y= 17 y=4 Divide both sides by 17. Simplify. Take the answer y = 4 and substitute 4 for y in the ﬁrst equation. −12x + 9y = 0 −12x + 9(4) = 0 First equation. Substitute 4 for y. −12x + 36 = 0 −12x = −36 Multiply. Subtract 36 from both sides. Divide both sides by −12 x=3 Hence, the solution is (x, y) = (3, 4). 11. Start with the given system. 27x − −3x − 6y 5y = = −96 22 We’ll concentrate on eliminating x. Multiply the second equation by 9, then add the results. 27x − 6y = −96 −27x − 45y = 198 − 51y = 102 Divide both sides by −51. −51y = 102 102 y= −51 y = −2 Divide both sides by −51. Simplify. Take the answer y = −2 and substitute −2 for y in the ﬁrst equation. 27x − 6y = −96 27x − 6(−2) = −96 27x + 12 = −96 27x = −108 x = −4 First equation. Substitute −2 for y. Multiply. Subtract 12 from both sides. Divide both sides by 27 Hence, the solution is (x, y) = (−4, −2). Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 248 13. Start with the given system. 2x − −3x + 6y 18y = = 28 −60 We’ll concentrate on eliminating y. Multiply the ﬁrst equation by 3, then add the results. 6x − 18y = 84 −3x + 18y = −60 3x = 24 Divide both sides by 3. 3x = 24 24 x= 3 x=8 Divide both sides by 3. Simplify. Take the answer x = 8 and substitute 8 for x in the ﬁrst equation. 2x − 6y = 28 2(8) − 6y = 28 First equation. Substitute 8 for x. 16 − 6y = 28 −6y = 12 Multiply. Subtract 16 from both sides. y = −2 Divide both sides by −6 Hence, the solution is (x, y) = (8, −2). 15. Start with the given system. −32x + 7y 8x − 4y = −238 = 64 We’ll concentrate on eliminating x. Multiply the second equation by 4, then add the results. −32x + 7y = −238 32x − 16y = 256 − 9y = 18 Divide both sides by −9. −9y = 18 18 y= −9 y = −2 Second Edition: 2012-2013 Divide both sides by −9. Simplify. 4.3. SOLVING SYSTEMS BY ELIMINATION 249 Take the answer y = −2 and substitute −2 for y in the ﬁrst equation. −32x + 7y = −238 −32x + 7(−2) = −238 First equation. Substitute −2 for y. −32x − 14 = −238 −32x = −224 Multiply. Add 14 to both sides. Divide both sides by −32 x=7 Hence, the solution is (x, y) = (7, −2). 17. Start with the given system. 3x − −2x − 7y 2y = = −75 −10 We’ll ﬁrst concentrate on eliminating the variable x. Multiply the ﬁrst equation by 2, the second equation by 3, then add the results. 6x − −6x − 14y 6y = = −150 −30 − 20y = −180 Divide both sides by −20. −20y = −180 −180 y= −20 y=9 Divide both sides by −20. Simplify. Take the answer y = 9 and substitute 9 for y in the ﬁrst equation (you could also make the substitution in the second equation). 3x − 7y = −75 3x − 7(9) = −75 3x − 63 = −75 3x = −12 −12 x= 3 x = −4 First equation. Substitute 9 for y. Multiply. Add 63 to both sides. Divide both sides by 3. Simplify. Hence, the solution is (x, y) = (−4, 9). Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 250 19. Start with the given system. 9x − 9y 2x − 6y = = −63 −34 We’ll ﬁrst concentrate on eliminating the variable x. Multiply the ﬁrst equation by −2, the second equation by 9, then add the results. −18x + 18x − 18y 54y = = 126 −306 − 36y = −180 Divide both sides by −36. −36y = −180 −180 y= −36 y=5 Divide both sides by −36. Simplify. Take the answer y = 5 and substitute 5 for y in the ﬁrst equation (you could also make the substitution in the second equation). 9x − 9y = −63 First equation. 9x − 9(5) = −63 9x − 45 = −63 Substitute 5 for y. Multiply. 9x = −18 −18 x= 9 x = −2 Add 45 to both sides. Divide both sides by 9. Simplify. Hence, the solution is (x, y) = (−2, 5). 21. Start with the given system. −9x − 2y 5x − 3y = 28 = −32 We’ll ﬁrst concentrate on eliminating the variable x. Multiply the ﬁrst equation by −5, the second equation by −9, then add the results. 45x + −45x + Second Edition: 2012-2013 10y 27y = = −140 288 37y = 148 4.3. SOLVING SYSTEMS BY ELIMINATION 251 Divide both sides by 37. 37y = 148 148 y= 37 y=4 Divide both sides by 37. Simplify. Take the answer y = 4 and substitute 4 for y in the ﬁrst equation (you could also make the substitution in the second equation). −9x − 2y = 28 −9x − 2(4) = 28 First equation. Substitute 4 for y. −9x − 8 = 28 −9x = 36 36 x= −9 x = −4 Multiply. Add 8 to both sides. Divide both sides by −9. Simplify. Hence, the solution is (x, y) = (−4, 4). 23. Start with the given system. −3x − 7x + 5y 7y = = −34 56 We’ll ﬁrst concentrate on eliminating the variable x. Multiply the ﬁrst equation by −7, the second equation by −3, then add the results. 21x + 35y −21x − 21y = = 238 −168 14y = 70 Divide both sides by 14. 14y = 70 70 y= 14 y=5 Divide both sides by 14. Simplify. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 252 Take the answer y = 5 and substitute 5 for y in the ﬁrst equation (you could also make the substitution in the second equation). −3x − 5y = −34 −3x − 5(5) = −34 First equation. Substitute 5 for y. −3x − 25 = −34 −3x = −9 −9 x= −3 x=3 Multiply. Add 25 to both sides. Divide both sides by −3. Simplify. Hence, the solution is (x, y) = (3, 5). 25. Start with the given system. 2x − 7x + 7y 6y −2 3 = = We’ll ﬁrst concentrate on eliminating the variable x. Multiply the ﬁrst equation by −7, the second equation by 2, then add the results. −14x + 14x + 49y 12y = = 14 6 61y = 20 Divide both sides by 61 to get y = 20/61. Next, we could substitute 20/61 for y in either equation and solve to ﬁnd x. However, in this case it is probably easier to perform elimination again. Start with the given system again. 2x − 7x + 7y 6y −2 3 = = This time we concentrate on eliminating the variable y. Multiply the ﬁrst equation by −6, the second equation by −7, then add the results. −12x + 42y −49x − 42y = = 12 −21 −61x = −9 Divide both sides by −61 to get x = 9/61. Hence, the solution is (x, y) = (9/61, 20/61). Check: First, store 9/61 in X with the following keystrokes. The result is shown in the ﬁrst image below. 9 ÷ 6 Second Edition: 2012-2013 1 STO X, T, θ, n ENTER 4.3. SOLVING SYSTEMS BY ELIMINATION 253 Store 20/61 in Y with the following keystrokes. The result is shown in the ﬁrst image below. 2 0 ÷ 6 1 STO ALPHA 1 ENTER Clear the calculator screen by pressing the CLEAR button, then enter the lefthand side of the ﬁrst equation with the following keystrokes. The result is shown in the second image below. 2 × X, T, θ, n − × 7 ALPHA 1 ENTER Enter the right-hand side of the second equation with the following keystrokes. The result is shown in the second image below. 7 × X, T, θ, n + × 6 ALPHA 1 ENTER The result in the second image shows that 2x − 7y = −2 and 7x + 6y = 3 for x = 9/61 and y = 20/61. The solution checks. 27. Start with the given system. 2x + −5x + 3y 5y = = −2 2 We’ll ﬁrst concentrate on eliminating the variable x. Multiply the ﬁrst equation by 5, the second equation by 2, then add the results. 10x + −10x + 15y 10y = −10 = 4 25y = −6 Divide both sides by 25 to get y = −6/25. Next, we could substitute −6/25 for y in either equation and solve to ﬁnd x. However, in this case it is probably easier to perform elimination again. Start with the given system again. 2x + −5x + 3y 5y = = −2 2 Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 254 This time we concentrate on eliminating the variable y. Multiply the ﬁrst equation by −5, the second equation by 3, then add the results. −10x − −15x + 15y 15y −25x = = 10 6 = 16 Divide both sides by −25 to get x = −16/25. Hence, the solution is (x, y) = (−16/25, −6/25). Check: First, store −16/25 in X with the following keystrokes. The result is shown in the ﬁrst image below. (-) 1 ÷ 6 2 5 STO X, T, θ, n ENTER Store −6/25 in Y with the following keystrokes. The result is shown in the ﬁrst image below. (-) 6 ÷ 2 5 STO ALPHA 1 ENTER Clear the calculator screen by pressing the CLEAR button, then enter the lefthand side of the ﬁrst equation with the following keystrokes. The result is shown in the second image below. × 2 X, T, θ, n + × 3 ALPHA 1 ENTER Enter the right-hand side of the second equation with the following keystrokes. The result is shown in the second image below. (-) 5 × X, T, θ, n + 5 × ALPHA 1 ENTER The result in the second image shows that 2x + 3y = −2 and −5x + 5y = 2 for x = −16/25 and y = −6/25. The solution checks. Second Edition: 2012-2013 4.3. SOLVING SYSTEMS BY ELIMINATION 255 29. Start with the given system. 9x + −7x − 4y 9y −4 3 = = We’ll ﬁrst concentrate on eliminating the variable x. Multiply the ﬁrst equation by 7, the second equation by 9, then add the results. 63x + −63x − 28y 81y = −28 = 27 − 53y = −1 Divide both sides by −53 to get y = 1/53. Next, we could substitute 1/53 for y in either equation and solve to ﬁnd x. However, in this case it is probably easier to perform elimination again. Start with the given system again. 9x + −7x − 4y 9y −4 3 = = This time we concentrate on eliminating the variable y. Multiply the ﬁrst equation by 9, the second equation by 4, then add the results. 81x + −28x − = −36 = 12 36y 36y = −24 53x Divide both sides by 53 to get x = −24/53. Hence, the solution is (x, y) = (−24/53, 1/53). Check: First, store −24/53 in X with the following keystrokes. The result is shown in the ﬁrst image below. (-) 2 ÷ 4 5 3 STO X, T, θ, n ENTER Store 1/53 in Y with the following keystrokes. The result is shown in the ﬁrst image below. 1 ÷ 5 3 STO ALPHA 1 ENTER Clear the calculator screen by pressing the CLEAR button, then enter the lefthand side of the ﬁrst equation with the following keystrokes. The result is shown in the second image below. 9 × X, T, θ, n + 4 × ALPHA 1 ENTER Enter the right-hand side of the second equation with the following keystrokes. The result is shown in the second image below. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 256 (-) × 7 − X, T, θ, n 9 × ALPHA 1 ENTER The result in the second image shows that 9x + 4y = −4 and −7x − 9y = 3 for x = −24/53 and y = 1/53. The solution checks. 31. Start with the given system. 2x + 2y 3x − 5y = = 4 3 We’ll ﬁrst concentrate on eliminating the variable x. Multiply the ﬁrst equation by −3, the second equation by 2, then add the results. −6x − 6x − 6y 10y = = −12 6 − 16y = −6 Divide both sides by −16 to get y = 3/8. Next, we could substitute 3/8 for y in either equation and solve to ﬁnd x. However, in this case it is probably easier to perform elimination again. Start with the given system again. 2x + 2y 3x − 5y = = 4 3 This time we concentrate on eliminating the variable y. Multiply the ﬁrst equation by 5, the second equation by 2, then add the results. 10x + 10y 6x − 10y = = 20 6 16x = 26 Divide both sides by 16 to get x = 13/8. Hence, the solution is (x, y) = (13/8, 3/8). Check: First, store 13/8 in X with the following keystrokes. The result is shown in the ﬁrst image below. 1 3 ÷ Second Edition: 2012-2013 8 STO X, T, θ, n ENTER 4.3. SOLVING SYSTEMS BY ELIMINATION 257 Store 3/8 in Y with the following keystrokes. The result is shown in the ﬁrst image below. 3 ÷ 8 STO 1 ALPHA ENTER Clear the calculator screen by pressing the CLEAR button, then enter the lefthand side of the ﬁrst equation with the following keystrokes. The result is shown in the second image below. 2 × X, T, θ, n + × 2 ALPHA 1 ENTER Enter the right-hand side of the second equation with the following keystrokes. The result is shown in the second image below. 3 × X, T, θ, n − × 5 ALPHA 1 ENTER The result in the second image shows that 2x + 2y = 4 and 3x − 5y = 3 for x = 13/8 and y = 3/8. The solution checks. 33. Start with the given system. x + 7y −8x − 56y = = −32 256 We’ll concentrate on eliminating x. Multiply the ﬁrst equation by 8, then add the results. 8x + 56y = −256 −8x − 56y = 256 0 = 0 Note that this last statement, 0 = 0, is true. Hence, the system has an inﬁnite number of solutions. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 258 35. Start with the given system. 16x − −8x + 16y 8y = −256 = 128 We’ll concentrate on eliminating x. Multiply the second equation by 2, then add the results. 16x − 16y = −256 −16x + 16y = 256 0 = 0 Note that this last statement, 0 = 0, is true. Hence, the system has an inﬁnite number of solutions. 37. Start with the given system. x − 4y 2x − 8y = = −37 54 We’ll concentrate on eliminating x. Multiply the ﬁrst equation by −2, then add the results. −2x + 8y = 74 2x − 8y = 54 0 = 128 Note that this last statement, 0 = 128, is false. Hence, the system has no solution. 39. Start with the given system. x + 9y −4x − 5y = 73 = −44 We’ll concentrate on eliminating x. Multiply the ﬁrst equation by 4, then add the results. 4x + 36y = 292 −4x − 5y = −44 31y = 248 Divide both sides by 31. 31y = 248 248 y= 31 y=8 Second Edition: 2012-2013 Divide both sides by 31. Simplify. 4.4. APPLICATIONS OF LINEAR SYSTEMS 259 Take the answer y = 8 and substitute 8 for y in the ﬁrst equation. x + 9y = 73 First equation. x + 9(8) = 73 x + 72 = 73 Substitute 8 for y. Multiply. x=1 Subtract 72 from both sides. Hence, the solution is (x, y) = (1, 8). 4.4 Applications of Linear Systems 1. In the solution, we address each step of the Requirements for Word Problem Solutions. 1. Set up a Variable Dictionary. Our variable dictionary will take the form of a diagram, naming the two complementary angles α and β. β α 2. Set up a System of Equations. The “second angle is 42 degrees larger than 3 times the ﬁrst angle” becomes β = 42 + 3α Secondly, the angles are complementary, meaning that the sum of the angles is 90◦ . α + β = 90 Thus, we have a system of two equations in two unknowns α and β. 3. Solve the System. Substitute 42 + 3α for β in α + β = 90. α + β = 90 α + (42 + 3α) = 90 4α + 42 = 90 4α = 48 α = 12 Substitute 42 + 3α for β. Combine like terms. Subtract 42 from both sides. Divide both sides by 4. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 260 4. Answer the Question. The ﬁrst angle is α = 12 degrees. The second angle is: β = 42 + 3α β = 42 + 3(12) Substitute 12 for α. β = 78 Simplify. 5. Look Back. Certainly 78◦ is 42◦ larger than 3 times 12◦ . Also, note that 12◦ + 78◦ = 90◦ , so the angles are complementary. We have the correct solution. 3. In the solution, we address each step of the Requirements for Word Problem Solutions. 1. Set up a Variable Dictionary. Our variable dictionary will take the form of a diagram, naming the width and length W and L, respectively. L W W L 2. Set up a System of Equations. The perimeter is found by summing the four sides of the rectangle. P =L+W +L+W P = 2L + 2W We’re told the perimeter is 116 inches, so we can substitute 116 for P in the last equation. 116 = 2L + 2W We can simplify this equation by dividing both sides by 2, giving the following result: L + W = 58 Secondly, we’re told that the “length is 28 inches more than twice the width.” This translates to: L = 28 + 2W Second Edition: 2012-2013 4.4. APPLICATIONS OF LINEAR SYSTEMS 261 3. Solve the System. As the last equation is already solved for L, let use the substitution method and substitute 28 + 2W for L in the equation L + W = 58. L + W = 58 (28 + 2W ) + W = 58 3W + 28 = 58 3W = 30 W = 10 Perimeter equation. Substitute 28 + 2W for L. Combine like terms. Subtract 28 from both sides. Divide both sides by 3. 4. Answer the Question. The width is W = 10 inches. To ﬁnd the length, substitute 10 for W in the equation L = 28 + 2W . L = 28 + 2W L = 28 + 2(10) Length equation. Substitute 10 for W . L = 28 + 20 L = 48 Multiply. Add. Thus, the length is L = 48 inches. 5. Look Back. Perhaps a picture, labeled with our answers might best demonstrate that we have the correct solution. Remember, we found that the width was 10 inches and the length was 48 inches. 48 10 10 48 Note that the perimeter is P = 48 + 10 + 48 + 10 = 116 inches. Secondly, note that the length (48 inches) is 28 inches more than twice the width. So we have the correct solution. 5. In the solution, we address each step of the Requirements for Word Problem Solutions. 1. Set up a Variable Dictionary. Let N represent the number of nickels and let Q represent the number of quarters. 2. Set up a System of Equations. Using a table to summarize information is a good strategy. In the ﬁrst column, we list the type of coin. The second column gives the number of each type of coin, and the third column contains the value (in cents) of the number of coins in her pocket. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 262 Number of Coins Value (in cents) Nickels N 5N Quarters Q 25Q Totals 59 635 Note that N nickels, valued at 5 cents apiece, are worth 5N cents. Similarly, Q quarters, valued at 25 cents apiece, are worth 25Q cents. Note also how we’ve change $6.35 to 635 cents. The second column of the table gives us our ﬁrst equation. N + Q = 59 The third column of the table gives us our second equation. 5N + 25Q = 635 3. Solve the System. Because both equations are in standard form Ax+By = C, we’ll use the elimination method to ﬁnd a solution. Because the question asks us to ﬁnd the number of quarters in her pocket, we’ll focus on eliminating the N -terms and keeping the Q-terms. −5N 5N − + 5Q = −295 25Q = 635 20Q = Multiply ﬁrst equation by −5. Second equation. 340 Add the equations. Dividing both sides of the last equation by 20 gives us Q = 17. 4. Answer the Question. The previous solution tells us that Maria has 17 quarters in her pocket. 5. Look Back. Again, summarizing results in a table might help us see if we have the correct solution. First, because we’re told that Maria has 59 coins in all, and we found that she had 17 quarters, this means that she must have 42 nickels. Number of Coins Value (in cents) Nickels 42 210 Quarters 17 425 Totals 59 635 42 nickels are worth 210 cents, and 17 quarters are worth 425 cents. That’s a total of 59 coins and 635 cents, or $6.35. Thus we have the correct solution. Second Edition: 2012-2013 4.4. APPLICATIONS OF LINEAR SYSTEMS 263 7. In the solution, we address each step of the Requirements for Word Problem Solutions. 1. Set up a Variable Dictionary. Let x be the number of pounds of cashews used and let y be the number of pounds of raisins used. 2. Set up a System of Equations. The following table summarizes the information given in the problem: Cost per pound Amount (pounds) Cost cashews $6.00 x 6.00x raisins $7.00 y 7.00y Totals $6.42 50 6.42(50) = 321.00 At $6.00 per pound, x pounds of cashews cost 6.00x. At $7.00 per pound, y pounds of raisins cost 7.00y. Finally, at $6.42 per pound, 50 pounds of a mixture of cashews and raisins will cost $6.42(50), or $321.00. The third column of the table gives us our ﬁrst equation. The total number of pounds of mixture is given by the following equation: x + y = 50 The fourth column of the table gives us our second equation. The total cost is the sum of the costs for purchasing the cashews and raisins. 6.00x + 7.00y = 321.00 Therefore, we have the following system of equations: x + y = 50 6.00x + 7.00y = 321.00 3. Solve the System. We can solve this system by substitution. Solve the ﬁrst equation for x. x + y = 50 First Equation. x = 50 − y Subtract y from both sides. Next, substitute 50 − y for x in the second equation and solve for y. 6.00x + 7.00y = 321.00 6.00(50 − y) + 7.00y = 321.00 300.00 − 6.00y + 7.00y = 321.00 300.00 + 1.00y = 321.00 1.00y = 21.00 y = 21 Second Equation. Substitute 50 − y for x. Distribute the 6.00. Combine like terms. Subtract 300.00 from both sides. Divide both sides by 1.00. Thus, there are 21 pounds of raisins in the mix. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 264 4. Answer the Question. The question asks for both amounts, cashews and raisins. Substitute 21 for y in the ﬁrst equation and solve for x. x + y = 50 First Equation. x + 21 = 50 x = 29 Substitute 21 for y. Subtract 21 from both sides. Thus, there are 29 pounds of cashews in the mix. 5. Look Back. First, note that the amount of cashews and raisins in the mix is 29 and 21 pounds respectively, so that the total mixture weighs 50 pounds as required. Let’s calculate the costs: for the cashews, 6.00(29), or $174.00, for the raisins, 7.00(21), or $147.00. Cost per pound Amount (pounds) Cost cashews $6.00 29 $174.00 raisins $7.00 21 $147.00 Totals $6.42 50 $321.00 Note that the total cost is $321.00, as required in the problem statement. Thus, our solution is correct. 9. In the solution, we address each step of the Requirements for Word Problem Solutions. 1. Set up a Variable Dictionary. Let D represent the number of dimes and let Q represent the number of quarters. 2. Set up a System of Equations. Using a table to summarize information is a good strategy. In the ﬁrst column, we list the type of coin. The second column gives the number of each type of coin, and the third column contains the value (in cents) of the number of coins in his pocket. Number of Coins Value (in cents) Dimes D 10D Quarters Q 25Q Totals 38 545 Note that D times, valued at 10 cents apiece, are worth 10D cents. Similarly, Q quarters, valued at 25 cents apiece, are worth 25Q cents. Note also how we’ve change $5.45 to 545 cents. Second Edition: 2012-2013 4.4. APPLICATIONS OF LINEAR SYSTEMS 265 The second column of the table gives us our ﬁrst equation. D + Q = 38 The third column of the table gives us our second equation. 10D + 25Q = 545 3. Solve the System. Because both equations are in standard form Ax+By = C, we’ll use the elimination method to ﬁnd a solution. Because the question asks us to ﬁnd the number of dimes in his pocket, we’ll focus on eliminating the Q-terms and keeping the D-terms. −25D 10D − + 25Q = 25Q = −950 545 Multiply ﬁrst equation by −25. Second equation. = −405 Add the equations. −15D Dividing both sides of the last equation by −15 gives us D = 27. 4. Answer the Question. The previous solution tells us that Roberto has 27 dimes in his pocket. 5. Look Back. Again, summarizing results in a table might help us see if we have the correct solution. First, because we’re told that Roberto has 38 coins in all, and we found that he had 27 dimes, this means that he must have 11 quarters. Number of Coins Value (in cents) Dimes 27 270 Quarters 11 275 Totals 38 545 27 dimes are worth 270 cents, and 11 quarters are worth 275 cents. That’s a total of 38 coins and 545 cents, or $5.45. Thus we have the correct solution. 11. In geometry, two angles that sum to 180◦ are called supplementary angles. If the second of two supplementary angles is 40 degrees larger than 3 times the ﬁrst angle, ﬁnd the degree measure of both angles. Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 266 13. In the solution, we address each step of the Requirements for Word Problem Solutions. 1. Set up a Variable Dictionary. Let C represent the amount invested in the certiﬁcate of deposit and M represent the amount invested in the mutual fund. 2. Set up a System of Equations. The following table summarizes the information given in the problem: Rate Amount invested Interest Certiﬁcate of Deposit 3% C 0.03C Mutual Fund 5% M 0.05M 20,000 780 Totals At 3%, the interest earned on a C dollars investment is found by taking 3% of C (i.e., 0.03C). Similarly, the interest earned on the mutual fund is 0.05M . The third column of the table gives us our ﬁrst equation. The total investment is $20,000. C + M = 20000 The fourth column of the table gives us our second equation. The total interest earned is the sum of the interest earned in each account. 0.03C + 0.05M = 780 Therefore, we have the following system of equations: C + M = 20000 0.03C + 0.05M = 780 3. Solve the System. We can solve this system by substitution. Solve the ﬁrst equation for C. C + M = 20000 First Equation. C = 20000 − M Subtract M from both sides. Next, substitute 20000 − M for C in the second equation and solve for M. 0.03C + 0.05M = 780 0.03(20000 − M ) + 0.05M = 780 600 − 0.03M + 0.05M = 780 600 + 0.02M = 780 0.02M = 180 M = 9000 Second Edition: 2012-2013 Second Equation. Substitute 20000 − M for C. Distribute the 0.03. Combine like terms. Subtract 600 from both sides. Divide both sides by 0.02. 4.4. APPLICATIONS OF LINEAR SYSTEMS 267 Thus, the amount invested in the mutual fund is M = $9, 000. 4. Answer the Question. The question asks us to ﬁnd the amount invested in each account. So, substitute 9000 for M in the ﬁrst equation and solve for C. C + M = 20000 First Equation. C + 9000 = 20000 C = 11000 Substitute 9000 for M . Subtract 9000 from both sides. Thus, the amount invested in the certiﬁcate of deposit is $11, 000. 5. Look Back. First, note that the investments in the certiﬁcate of deposit and the mutual fund, $11000 and $9000 respectively, total $20,000. Let’s calculate the interest on each investment: 3% of $11000 is $330 and 5% of $9000 is $450. Rate Amount invested Interest Certiﬁcate of Deposit 3% 11,000 330 Mutual Fund 5% 9,000 450 20,000 780 Totals Note that the total interest is $780, as required in the problem statement. Thus, our solution is correct. 15. In the solution, we address each step of the Requirements for Word Problem Solutions. 1. Set up a Variable Dictionary. Our variable dictionary will take the form of a diagram, naming the width and length W and L, respectively. L W W L 2. Set up a System of Equations. The perimeter is found by summing the four sides of the rectangle. P =L+W +L+W P = 2L + 2W Second Edition: 2012-2013 CHAPTER 4. SYSTEMS 268 We’re told the perimeter is 376 centimeters, so we can substitute 376 for P in the last equation. 376 = 2L + 2W We can simplify this equation by dividing both sides by 2, giving the following result: L + W = 188 Secondly, we’re told that the “length is 12 centimeters less than three times the width.” This translates to: L = 3W − 12 3. Solve the System. As the last equation is already solved for L, let use the substitution method and substitute 3W − 12 for L in the equation L + W = 188. L + W = 188 Perimeter equation. (3W − 12) + W = 188 4W − 12 = 188 Substitute 3W − 12 for L. Combine like terms. 4W = 200 W = 50 Add 12 to both sides. Divide both sides by 4. 4. Answer the Question. The width is W = 50 centimeters. To ﬁnd the length, substitute 50 for W in the equation L = 3W − 12. L = 3W − 12 L = 3(50) − 12 Length equation. Substitute 50 for W . L = 150 − 12 L = 138 Multiply. Subtract. Thus, the length is L = 138 centimeters. 5. Look Back. Perhaps a picture, labeled with our answers might best demonstrate that we have the correct solution. Remember, we found that the width was 50 centimeters and the length was 138 centimeters. 138 50 50 138 Note that the perimeter is P = 138 + 50 + 138 + 50 = 376 centimeters. Secondly, note that the length (138 centimeters) is 12 centimeters less than three times the width. So we have the correct solution. Second Edition: 2012-2013 Chapter 5 Polynomials 5.1 Functions 1. Consider again the relation R. R = {(7, 4), (2, 4), (4, 2), (8, 5)} To form the domain, we take the ﬁrst element of each ordered pair and put it into a set. {7, 2, 4, 8} However, in listing the ﬁnal answer, we should eliminate duplicate elements and then sort the numbers in numerical order, from smallest to largest. Domain = {2, 4, 7, 8} To ﬁnd the range, we take the second element of each ordered pair and put it in a set. {4, 4, 2, 5} However, in listing the ﬁnal answer, we should eliminate duplicate elements and then sort the numbers in numerical order, from smallest to largest. Range = {2, 4, 5} 3. Consider again the relation T. T = {(7, 2), (3, 1), (9, 4), (8, 1)} To form the domain, we take the ﬁrst element of each ordered pair and put it into a set. {7, 3, 9, 8} 269 CHAPTER 5. POLYNOMIALS 270 However, in listing the ﬁnal answer, we should eliminate duplicate elements and then sort the numbers in numerical order, from smallest to largest. Domain = {3, 7, 8, 9} To ﬁnd the range, we take the second element of each ordered pair and put it in a set. {2, 1, 4, 1} However, in listing the ﬁnal answer, we should eliminate duplicate elements and then sort the numbers in numerical order, from smallest to largest. Range = {1, 2, 4} 5. Consider again the relation T. T = {(4, 7), (4, 8), (5, 0), (0, 7)} To form the domain, we take the ﬁrst element of each ordered pair and put it into a set. {4, 4, 5, 0} However, in listing the ﬁnal answer, we should eliminate duplicate elements and then sort the numbers in numerical order, from smallest to largest. Domain = {0, 4, 5} To ﬁnd the range, we take the second element of each ordered pair and put it in a set. {7, 8, 0, 7} However, in listing the ﬁnal answer, we should eliminate duplicate elements and then sort the numbers in numerical order, from smallest to largest. Range = {0, 7, 8} 7. Consider again the relation given graphically. y 5 A B x −5 5 C D −5 Second Edition: 2012-2013 5.1. FUNCTIONS 271 Note the coordinates of each point: A = (2, 4), B = (−2, 2), C = (−2, −2), and D = (2, −2). To form the domain, we take the ﬁrst element of each ordered pair and put it into a set. {2, −2, −2, 2} However, in listing the ﬁnal answer, we should eliminate duplicate elements and then sort the numbers in numerical order, from smallest to largest. Domain = {−2, 2} To ﬁnd the range, we take the second element of each ordered pair and put it in a set. {4, 2, −2, −2} However, in listing the ﬁnal answer, we should eliminate duplicate elements and then sort the numbers in numerical order, from smallest to largest. Range = {−2, 2, 4} 9. Consider again the relation given graphically. y B 5 A x −5 5 C D −5 Note the coordinates of each point: A = (1, 2), B = (−1, 4), C = (−4, −2), and D = (2, −2). To form the domain, we take the ﬁrst element of each ordered pair and put it into a set. {1, −1, −4, 2} However, in listing the ﬁnal answer, we should eliminate duplicate elements and then sort the numbers in numerical order, from smallest to largest. Domain = {−4, −1, 1, 2} To ﬁnd the range, we take the second element of each ordered pair and put it in a set. {2, 4, −2, −2} Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 272 However, in listing the ﬁnal answer, we should eliminate duplicate elements and then sort the numbers in numerical order, from smallest to largest. Range = {−2, 2, 4} 11. Consider again the relation. R = {(−6, −4), (−4, −4), (1, −4)} List the elements of the domain on the left, the elements of the range on the right, then use arrows to indicate the connection between the ﬁrst and second elements of each ordered pair. R −6 −4 1 −4 Note that each domain element is paired with exactly one range element. Hence, R is a function. 13. Consider again the relation. T = {(−1, −7), (2, −5), (4, −2)} List the elements of the domain on the left, the elements of the range on the right, then use arrows to indicate the connection between the ﬁrst and second elements of each ordered pair. T −1 2 4 −7 −5 −2 Note that each domain element is paired with exactly one range element. Hence, T is a function. 15. Consider again the relation. T = {(−9, 1), (1, 6), (1, 8)} List the elements of the domain on the left, the elements of the range on the right, then use arrows to indicate the connection between the ﬁrst and second elements of each ordered pair. Second Edition: 2012-2013 5.1. FUNCTIONS 273 T −9 1 1 6 8 Note that the domain element 1 is paired with two range elements, 1 and 6. Hence, the relation T is not a function. 17. Consider again the relation. R = {(−7, −8), (−7, −6), (−5, 0)} List the elements of the domain on the left, the elements of the range on the right, then use arrows to indicate the connection between the ﬁrst and second elements of each ordered pair. R −7 −5 −8 −6 0 Note that the domain element −7 is paired with two range elements, −8 and −6. Hence, the relation R is not a function. 19. Consider again the relation. y 5 C B A −1 −1 5 x Create a mapping diagram for the points A = (1, 2), B = (2, 3), and C = (4, 4). List the elements of the domain on the left, the elements of the range on the right, then use arrows to indicate the connection between the ﬁrst and second elements of each ordered pair. Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 274 1 2 4 2 3 4 Note that each domain element is paired with exactly one range element. Hence, the relation is a function. 21. Consider again the relation. y 5 C B A −1 −1 5 x Create a mapping diagram for the points A = (1, 1), B = (1, 2), and C = (2, 4). List the elements of the domain on the left, the elements of the range on the right, then use arrows to indicate the connection between the ﬁrst and second elements of each ordered pair. 1 2 1 2 4 Note that the domain element 1 is paired with two range elements, 1 and 2. Hence, the relation is not a function. 23. Given f (x) = |6x − 9|, to evaluate f (8), ﬁrst restate the function notation, then replace each occurrence of the variable with open parentheses. f (x) = |6x − 9| Original function notation. f ( ) = |6( ) − 9| Replace each occurrence of x with open parentheses. Second Edition: 2012-2013 5.1. FUNCTIONS 275 Now substitute 8 for x in the open parentheses prepared in the last step. f (8) = |6(8) − 9| Substitute 8 for x in the open parentheses positions. f (8) = |48 − 9| f (8) = |39| Multiply: 6(8) = 48. Simplify. f (8) = 39 Take absolute value. Hence, f (8) = 39; i.e., f sends 8 to 39. 25. Given f (x) = −2x2 +8, to evaluate f (3), ﬁrst restate the function notation, then replace each occurrence of the variable with open parentheses. f (x) = −2x2 + 8 2 f ( ) = −2( ) + 8 Original function notation. Replace each occurrence of x with open parentheses. Now substitute 3 for x in the open parentheses prepared in the last step. f (3) = −2(3)2 + 8 Substitute 3 for x in the open parentheses positions. f (3) = −2(9) + 8 f (3) = −18 + 8 Exponent ﬁrst: (3)2 = 9 Multiply: −2(9) = −18 and 0(3) = 0 f (3) = −10 Simplify. Hence, f (3) = −10; i.e., f sends 3 to −10. 27. Given f (x) = −3x2 + 4x + 1, to evaluate f (2), ﬁrst restate the function notation, then replace each occurrence of the variable with open parentheses. f (x) = −3x2 + 4x + 1 2 f ( ) = −3( ) + 4( ) + 1 Original function notation. Replace each occurrence of x with open parentheses. Now substitute 2 for x in the open parentheses prepared in the last step. f (2) = −3(2)2 + 4(2) + 1 Substitute 2 for x in the open parentheses positions. f (2) = −3(4) + 4(2) + 1 f (2) = −12 + 8 + 1 Exponent ﬁrst: (2)2 = 4 Multiply: −3(4) = −12 and 4(2) = 8 Simplify. f (2) = −3 Hence, f (2) = −3; i.e., f sends 2 to −3. Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 276 29. Given f (x) = |5x+9|, to evaluate f (−8), ﬁrst restate the function notation, then replace each occurrence of the variable with open parentheses. f (x) = |5x + 9| f ( ) = |5( ) + 9| Original function notation. Replace each occurrence of x with open parentheses. Now substitute −8 for x in the open parentheses prepared in the last step. f (−8) = |5(−8) + 9| f (−8) = | − 40 + 9| Substitute −8 for x in the open parentheses positions. Multiply: 5(−8) = −40. f (−8) = | − 31| f (−8) = 31 Simplify. Take absolute value. Hence, f (−8) = 31; i.e., f sends −8 to 31. √ 31. Given f (x) = x − 6, to evaluate f (42), ﬁrst restate the function notation, then replace each occurrence of the variable with open parentheses. √ Original function notation. f (x) = x − 6 f( ) = ( ) − 6 Replace each occurrence of x with open parentheses. Now substitute 42 for x in the open parentheses prepared in the last step. Substitute 42 for x in the open f (42) = (42) − 6 parentheses positions. √ f (42) = 36 Simplify. √ f (42) = 6 Take square root: 36 = 6 Hence, f (42) = 6; i.e., f sends 42 to 6. √ 33. Given f (x) = x − 7, to evaluate f (88), ﬁrst restate the function notation, then replace each occurrence of the variable with open parentheses. √ Original function notation. f (x) = x − 7 Replace each occurrence of x with f( ) = ( ) − 7 open parentheses. Now substitute 88 for x in the open parentheses prepared in the last step. Substitute 88 for x in the open f (88) = (88) − 7 parentheses positions. √ f (88) = 81 Simplify. √ f (88) = 9 Take square root: 81 = 9 Second Edition: 2012-2013 5.1. FUNCTIONS 277 Hence, f (88) = 9; i.e., f sends 88 to 9. 35. Given f (x) = −4x + 6, to evaluate f (8), ﬁrst restate the function notation, then replace each occurrence of the variable with open parentheses. f (x) = −4x + 6 Original function notation. f ( ) = −4( ) + 6 Replace each occurrence of x with open parentheses. Now substitute 8 for x in the open parentheses prepared in the last step. f (8) = −4(8) + 6 Substitute 8 for x in the open parentheses positions. f (8) = −32 + 6 f (8) = −26 Multiply: −4(8) = −32 Add: −32 + 6 = −26 Hence, f (8) = −26; i.e., f sends 8 to −26. 37. Given f (x) = −6x + 7, to evaluate f (8), ﬁrst restate the function notation, then replace each occurrence of the variable with open parentheses. f (x) = −6x + 7 f ( ) = −6( ) + 7 Original function notation. Replace each occurrence of x with open parentheses. Now substitute 8 for x in the open parentheses prepared in the last step. f (8) = −6(8) + 7 f (8) = −48 + 7 Substitute 8 for x in the open parentheses positions. Multiply: −6(8) = −48 f (8) = −41 Add: −48 + 7 = −41 Hence, f (8) = −41; i.e., f sends 8 to −41. 39. Given f (x) = −2x2 + 3x + 2 and g(x) = 3x2 + 5x − 5, to evaluate f (3), ﬁrst choose the function f , then replace each occurrence of the variable with open parentheses. f (x) = −2x2 + 3x + 2 2 f ( ) = −2( ) + 3( ) + 2 Original function notation. Replace each occurrence of x with open parentheses. Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 278 Now substitute 3 for x in the open parentheses prepared in the last step. f (3) = −2(3)2 + 3(3) + 2 Substitute 3 for x in the open parentheses positions. f (3) = −2(9) + 3(3) + 2 Exponent ﬁrst: (3)2 = 9 f (3) = −18 + 9 + 2 Multiply: −2(9) = −18 and 3(3) = 9 f (3) = −7 Simplify. Hence, f (3) = −7; i.e., f sends 3 to −7. To evaluate g(3), repeat the same procedure, this time using the function g. g(x) = 3x2 + 5x − 5 2 g( ) = 3( ) + 5( ) − 5 Original function notation. Replace each occurrence of x with open parentheses. Now substitute 3 for x in the open parentheses prepared in the last step. g(3) = 3(3)2 + 5(3) − 5 Substitute 3 for x in the open parentheses positions. g(3) = 3(9) + 5(3) − 5 Exponent ﬁrst: (3)2 = 9 g(3) = 27 + 15 − 5 Multiply: 3(9) = 27 and 5(3) = 15 g(3) = 37 Simplify. Hence, g(3) = 37; i.e., g sends 3 to 37. 41. Given f (x) = 6x − 2 and g(x) = −8x + 9, to evaluate f (−7), ﬁrst choose the function f (x) = 6x − 2, then replace each occurrence of the variable with open parentheses. f (x) = 6x − 2 f ( ) = 6( ) − 2 Original function notation. Replace each occurrence of x with open parentheses. Now substitute −7 for x in the open parentheses prepared in the last step. f (−7) = 6(−7) − 2 f (−7) = −42 − 2 Substitute −7 for x in the open parentheses positions. Multiply: 6(−7) = −42 f (−7) = −44 Simplify. Second Edition: 2012-2013 5.1. FUNCTIONS 279 Hence, f (−7) = −44; i.e., f sends −7 to −44. Now, repeat the procedure, using the function g. g(x) = −8x + 9 g( ) = −8( ) + 9 Original function notation. Replace each occurrence of x with open parentheses. Now substitute −7 for x in the open parentheses prepared in the last step. g(−7) = −8(−7) + 9 g(−7) = 56 + 9 Substitute −7 for x in the open parentheses positions. Multiply: −8(−7) = 56 g(−7) = 65 Simplify. Hence, g(−7) = 65; i.e., g sends −7 to 65. 43. Given f (x) = 4x−3 and g(x) = −3x+8, to evaluate f (−3), ﬁrst choose the function f , then replace each occurrence of the variable with open parentheses. f (x) = 4x − 3 f ( ) = 4( ) − 3 Original function notation. Replace each occurrence of x with open parentheses. Now substitute −3 for x in the open parentheses prepared in the last step. f (−3) = 4(−3) − 3 f (−3) = −12 − 3 Substitute −3 for x in the open parentheses positions. Multiply: 4(−3) = −12 f (−3) = −15 Simplify. Hence, f (−3) = −15; i.e., f sends −3 to −15. To evaluate g(−3), repeat the same procedure, this time using the function g. g(x) = −3x + 8 g( ) = −3( ) + 8 Original function notation. Replace each occurrence of x with open parentheses. Now substitute −3 for x in the open parentheses prepared in the last step. g(−3) = −3(−3) + 8 g(−3) = 9 + 8 Substitute −3 for x in the open parentheses positions. Multiply: −3(−3) = 9 g(−3) = 17 Simplify. Hence, g(−3) = 17; i.e., g sends −3 to 17. Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 280 45. Given f (x) = −2x2 + 5x − 9 and g(x) = −2x2 + 3x − 4, to evaluate g(−2), ﬁrst choose the function g, then replace each occurrence of the variable with open parentheses. g(x) = −2x2 + 3x − 4 Original function notation. 2 g( ) = −2( ) + 3( ) − 4 Replace each occurrence of x with open parentheses. Now substitute −2 for x in the open parentheses prepared in the last step. g(−2) = −2(−2)2 + 3(−2) − 4 Substitute −2 for x in the open parentheses positions. g(−2) = −2(4) + 3(−2) − 4 g(−2) = −8 − 6 − 4 Exponent ﬁrst: (−2)2 = 4 Multiply: −2(4) = −8 g(−2) = −18 and 3(−2) = −6 Simplify. Hence, g(−2) = −18; i.e., g sends −2 to −18. To ﬁnd f (−2), repeat the procedure, this time using f . f (x) = −2x2 + 5x − 9 Original function notation. 2 f ( ) = −2( ) + 5( ) − 9 Replace each occurrence of x with open parentheses. Now substitute −2 for x in the open parentheses prepared in the last step. f (−2) = −2(−2)2 + 5(−2) − 9 Substitute −2 for x in the open parentheses positions. f (−2) = −2(4) + 5(−2) − 9 Exponent ﬁrst: (−2)2 = 4 f (−2) = −8 − 10 − 9 Multiply: −2(4) = −8 and 5(−2) = −10 f (−2) = −27 Simplify. Hence, f (−2) = −27; i.e., f sends −2 to −27. 5.2 Polynomials 1. When a term is a product of a number and one or more variables, the number in front of the variables is called the coeﬃcient of the term. Consequently, the coeﬃcient of the term 3v 5 u6 is 3. The degree of a term is the sum of the exponents on each variable of the term. Consequently, the degree of the term 3v 5 u6 is: Degree = 5 + 6 = 11 Second Edition: 2012-2013 5.2. POLYNOMIALS 281 3. When a term is a product of a number and one or more variables, the number in front of the variables is called the coeﬃcient of the term. Consequently, the coeﬃcient of the term −5v 6 is −5. The degree of a term is the sum of the exponents on each variable of the term. Consequently, the degree of the term −5v 6 is 6. 5. When a term is a product of a number and one or more variables, the number in front of the variables is called the coeﬃcient of the term. Consequently, the coeﬃcient of the term 2u7 x4 d5 is 2. The degree of a term is the sum of the exponents on each variable of the term. Consequently, the degree of the term 2u7 x4 d5 is: Degree = 7 + 4 + 5 = 16 7. The terms in an expression are separated by plus or minus signs. There is only one term in the expression, so −7b9 c3 is a monomial. 9. The terms in an expression are separated by plus or minus signs. There are exactly two terms in the expression, so 4u + 7v is a binomial. 11. The terms in an expression are separated by plus or minus signs. There are exactly three terms in the expression, so 3b4 − 9bc + 9c2 is a trinomial. 13. The terms in an expression are separated by plus or minus signs. There are exactly two terms in the expression, so 5s2 + 9t7 is a binomial. 15. The terms in an expression are separated by plus or minus signs. There are exactly three terms in the expression, so 2u3 − 5uv − 4v 4 is a trinomial. 17. To arrange −2x7 − 9x13 − 6x12 − 7x17 in descending powers of x, we must begin with the term with the largest exponent, then the next largest exponent, etc. Thus, arranging in descending powers, we arrive at: −7x17 − 9x13 − 6x12 − 2x7 19. To arrange 8x6 + 2x15 − 3x11 − 2x2 in descending powers of x, we must begin with the term with the largest exponent, then the next largest exponent, etc. Thus, arranging in descending powers, we arrive at: 2x15 − 3x11 + 8x6 − 2x2 Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 282 21. To arrange 7x17 +3x4 −2x12 +8x14 in ascending powers of x, we must begin with the term with the smallest exponent, then the next smallest exponent, etc. Thus, arranging in ascending powers, we arrive at: 3x4 − 2x12 + 8x14 + 7x17 23. To arrange 2x13 + 3x18 + 8x7 + 5x4 in ascending powers of x, we must begin with the term with the smallest exponent, then the next smallest exponent, etc. Thus, arranging in ascending powers, we arrive at: 5x4 + 8x7 + 2x13 + 3x18 25. In order to arrange our answer in descending powers of x, we want to place the term with the highest power of x ﬁrst and the term with the lowest power of x last. We use the commutative and associative properties to change the order and regroup, then we combine like terms. − 5x + 3 − 6x3 + 5x2 − 9x + 3 − 3x2 + 6x3 = (−6x3 + 6x3 ) + (5x2 − 3x2 ) + (−5x − 9x) + (3 + 3) = 2x2 − 14x + 6 27. In order to arrange our answer in descending powers of x, we want to place the term with the highest power of x ﬁrst and the term with the lowest power of x last. We use the commutative and associative properties to change the order and regroup, then we combine like terms. 4x3 + 6x2 − 8x + 1 + 8x3 − 7x2 + 5x − 8 = (4x3 + 8x3 ) + (6x2 − 7x2 ) + (−8x + 5x) + (1 − 8) = 12x3 − x2 − 3x − 7 29. In order to arrange our answer in descending powers of x, we want to place the term with the highest power of x ﬁrst and the term with the lowest power of x last. We use the commutative and associative properties to change the order and regroup, then we combine like terms. x2 + 9x − 3 + 7x2 − 3x − 8 = (x2 + 7x2 ) + (9x − 3x) + (−3 − 8) = 8x2 + 6x − 11 Second Edition: 2012-2013 5.2. POLYNOMIALS 283 31. In order to arrange our answer in descending powers of x, we want to place the term with the highest power of x ﬁrst and the term with the lowest power of x last. We use the commutative and associative properties to change the order and regroup, then we combine like terms. 8x + 7 + 2x2 − 8x − 3x3 − x2 = (−3x3 ) + (2x2 − x2 ) + (8x − 8x) + (7) = −3x3 + x2 + 7 33. We’ll arrange our answer in descending powers of x, so we place the term with the highest power of x ﬁrst and the term with the lowest power of x last. We use the commutative and associative properties to change the order and regroup, then we combine like terms. −8x2 − 4xz − 2z 2 − 3x2 − 8xz + 2z 2 = (−8x2 − 3x2 ) + (−4xz − 8xz) + (−2z 2 + 2z 2 ) = −11x2 − 12xz 35. We’ll arrange our answer in descending powers of u, so we place the term with the highest power of u ﬁrst and the term with the lowest power of u last. We use the commutative and associative properties to change the order and regroup, then we combine like terms. − 6u3 + 4uv 2 − 2v 3 − u3 + 6u2 v − 5uv 2 = (−6u3 − u3 ) + (6u2 v) + (4uv 2 − 5uv 2 ) + (−2v 3 ) = −7u3 + 6u2 v − uv 2 − 2v 3 37. We’ll arrange our answer in descending powers of b, so we place the term with the highest power of b ﬁrst and the term with the lowest power of b last. We use the commutative and associative properties to change the order and regroup, then we combine like terms. − 4b2 c − 3bc2 − 5c3 + 9b3 − 3b2 c + 5bc2 = (9b3 ) + (−4b2 c − 3b2 c) + (−3bc2 + 5bc2 ) + (−5c3 ) = 9b3 − 7b2 c + 2bc2 − 5c3 39. We’ll arrange our answer in descending powers of y, so we place the term with the highest power of y ﬁrst and the term with the lowest power of y last. Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 284 We use the commutative and associative properties to change the order and regroup, then we combine like terms. −8y 2 + 6yz − 7z 2 − 2y 2 − 3yz − 9z 2 = (−8y 2 − 2y 2 ) + (6yz − 3yz) + (−7z 2 − 9z 2 ) = −10y 2 + 3yz − 16z 2 41. We’ll arrange our answer in descending powers of b, so we place the term with the highest power of b ﬁrst and the term with the lowest power of b last. We use the commutative and associative properties to change the order and regroup, then we combine like terms. 7b2 c + 8bc2 − 6c3 − 4b3 + 9bc2 − 6c3 = (−4b3 ) + (7b2 c) + (8bc2 + 9bc2 ) + (−6c3 − 6c3 ) = −4b3 + 7b2 c + 17bc2 − 12c3 43. We’ll arrange our answer in descending powers of a, so we place the term with the highest power of a ﬁrst and the term with the lowest power of a last. We use the commutative and associative properties to change the order and regroup, then we combine like terms. 9a2 + ac − 9c2 − 5a2 − 2ac + 2c2 = (9a2 − 5a2 ) + (ac − 2ac) + (−9c2 + 2c2 ) = 4a2 − ac − 7c2 45. To help determine the degree, take the polynomial 3x15 + 4 + 8x3 − 8x19 and arrange it in descending powers of x: −8x19 + 3x15 + 8x3 + 4 Thus, its now easy to see that the term −8x19 is the term with the highest degree. Hence, the degree of −8x19 + 3x15 + 8x3 + 4 is 19. 47. To help determine the degree, take the polynomial 7x10 − 3x18 + 9x4 − 6 and arrange it in descending powers of x: −3x18 + 7x10 + 9x4 − 6 Thus, its now easy to see that the term −3x18 is the term with the highest degree. Hence, the degree of −3x18 + 7x10 + 9x4 − 6 is 18. Second Edition: 2012-2013 5.2. POLYNOMIALS 285 49. To help determine the degree, take the polynomial −2 − x7 − 5x5 + x10 and arrange it in descending powers of x: x10 − x7 − 5x5 − 2 Thus, its now easy to see that the term x10 is the term with the highest degree. Hence, the degree of x10 − x7 − 5x5 − 2 is 10. 51. Given f (x) = 5x3 + 4x2 − 6, to evaluate f (−1), ﬁrst restate the function notation, then replace each occurrence of the variable with open parentheses. f (x) = 5x3 + 4x2 − 6 3 2 f ( ) = 5( ) + 4( ) − 6 Original function notation. Replace each occurrence of x with open parentheses. Now substitute −1 for x in the open parentheses prepared in the last step. f (−1) = 5(−1)3 + 4(−1)2 − 6 Substitute −1 for x in the open parentheses positions. f (−1) = 5(−1) + 4(1) − 6 Exponents ﬁrst: (−1)3 = −1 f (−1) = −5 + 4 − 6 and (−1)2 = 1 Multiply: 5(−1) = −5, and 4(1) = 4 f (−1) = −7 Simplify. Hence, f (−1) = −7; i.e., f sends −1 to −7. 53. Given f (x) = 5x4 − 4x − 6, to evaluate f (−2), ﬁrst restate the function notation, then replace each occurrence of the variable with open parentheses. f (x) = 5x4 − 4x − 6 4 f ( ) = 5( ) − 4( ) − 6 Original function notation. Replace each occurrence of x with open parentheses. Now substitute −2 for x in the open parentheses prepared in the last step. f (−2) = 5(−2)4 − 4(−2) − 6 Substitute −2 for x in the open parentheses positions. f (−2) = 5(16) − 4(−2) − 6 f (−2) = 80 + 8 − 6 Exponents ﬁrst: (−2)4 = 16 Multiply: 5(16) = 80, and −4(−2) = 8 f (−2) = 82 Simplify. Hence, f (−2) = 82; i.e., f sends −2 to 82. Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 286 55. Given f (x) = 3x4 + 5x3 − 9, to evaluate f (−2), ﬁrst restate the function notation, then replace each occurrence of the variable with open parentheses. f (x) = 3x4 + 5x3 − 9 4 3 f ( ) = 3( ) + 5( ) − 9 Original function notation. Replace each occurrence of x with open parentheses. Now substitute −2 for x in the open parentheses prepared in the last step. f (−2) = 3(−2)4 + 5(−2)3 − 9 Substitute −2 for x in the open parentheses positions. f (−2) = 3(16) + 5(−8) − 9 Exponents ﬁrst: (−2)4 = 16 and (−2)3 = −8 f (−2) = 48 − 40 − 9 Multiply: 3(16) = 48, and 5(−8) = −40 f (−2) = −1 Simplify. Hence, f (−2) = −1; i.e., f sends −2 to −1. 57. Given f (x) = 3x4 − 5x2 + 8, to evaluate f (−1), ﬁrst restate the function notation, then replace each occurrence of the variable with open parentheses. f (x) = 3x4 − 5x2 + 8 4 2 f ( ) = 3( ) − 5( ) + 8 Original function notation. Replace each occurrence of x with open parentheses. Now substitute −1 for x in the open parentheses prepared in the last step. f (−1) = 3(−1)4 − 5(−1)2 + 8 Substitute −1 for x in the open parentheses positions. f (−1) = 3(1) − 5(1) + 8 Exponents ﬁrst: (−1)4 = 1 and (−1)2 = 1 f (−1) = 3 − 5 + 8 Multiply: 3(1) = 3, and −5(1) = −5 f (−1) = 6 Simplify. Hence, f (−1) = 6; i.e., f sends −1 to 6. 59. Given f (x) = −2x3 + 4x − 9, to evaluate f (2), ﬁrst restate the function notation, then replace each occurrence of the variable with open parentheses. f (x) = −2x3 + 4x − 9 3 f ( ) = −2( ) + 4( ) − 9 Second Edition: 2012-2013 Original function notation. Replace each occurrence of x with open parentheses. 5.2. POLYNOMIALS 287 Now substitute 2 for x in the open parentheses prepared in the last step. f (2) = −2(2)3 + 4(2) − 9 Substitute 2 for x in the open parentheses positions. f (2) = −2(8) + 4(2) − 9 Exponents ﬁrst: (2)3 = 8 f (2) = −16 + 8 − 9 Multiply: −2(8) = −16, and 4(2) = 8 Simplify. f (2) = −17 Hence, f (2) = −17; i.e., f sends 2 to −17. 61. Enter the equation p(x) = −2x2 + 8x + 32 into Y1 in the Y= menu, then select 6:ZStandard to produce the following image. Because the coeﬃcient of the leading term is −2, the parabola opens downward. Hence, the vertex must lie oﬀ the top of the screen. After some experimentation, we settled on the following WINDOW parameters, then pushed the GRAPH button to produce the accompanying graph. Follow the Calculator Submission Guidelines in reporting the answer on our homework. Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 288 y 50 −10 p(x) = −2x2 + 8x + 32 10 x −50 63. Enter the equation p(x) = 3x2 − 8x − 35 into Y1 in the Y= menu, then select 6:ZStandard to produce the following image. Because the coeﬃcient of the leading term is 3, the parabola opens upward. Hence, the vertex must lie oﬀ the bottom of the screen. After some experimentation, we settled on the following WINDOW parameters, then pushed the GRAPH button to produce the accompanying graph. Follow the Calculator Submission Guidelines in reporting the answer on our homework. Second Edition: 2012-2013 5.2. POLYNOMIALS 289 y 50 −10 10 x p(x) = 3x2 − 8x − 35 −50 65. Enter the function p(x) = x3 − 4x2 − 11x + 30 in the Y= menu (see ﬁrst image below), then set the given WINDOW parameters (see second image below). Push the GRAPH button to produce the graph (see third image below). Use the Calculator Submission Guidelines when reporting your solution. 1. Draw axes with a ruler. 50 2. Label the horizontal axis x and the vertical axis y. 3. Indicate the WINDOW parameters Xmin, Xmax, Ymin, and Ymax, at the end of each axis. 4. Freehand the curve and label it with its equation. −10 yp(x) = x3 − 4x2 − 11x + 40 10 x −50 67. Enter the function p(x) = x4 − 10x3 + 250x − 525 in the Y= menu (see ﬁrst image below), then set the given WINDOW parameters (see second image below). Push the GRAPH button to produce the graph (see third image below). Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 290 Use the Calculator Submission Guidelines when reporting your solution. 1. Draw axes with a ruler. p(x) = x4 − 10x3 − 4x2 + 250x − 525 y 500 2. Label the horizontal axis x and the vertical axis y. 3. Indicate the WINDOW parameters Xmin, Xmax, Ymin, and Ymax, at the end of each axis. −10 4. Freehand the curve and label it with its equation. 5.3 10 x −1000 Applications of Polynomials 1. To ﬁnd the ﬁrm’s revenue when it spends $10,000 on advertising, locate 10 on the horizontal axis (the horizontal axis is measured in thousands of dollars), draw a vertical arrow to the curve, then a horizontal arrow to the vertical axis. It appears that this last arrow points at a number between 7,400 and 7,500 on the vertical axis. We’ll guess 7,450. Because the vertical axis is measured in thousands of dollars, the ﬁrm’s revenue is approximately $7,450,000. Second Edition: 2012-2013 5.3. APPLICATIONS OF POLYNOMIALS 291 R (thousands of dollars) 8,500 8,000 7,500 7,000 6,500 6,000 x (thousands of dollars) 0 5 10 15 20 25 30 To use the polynomial to ﬁnd the ﬁrm’s revenue, substitute 10 for x. R(x) = −4.1x2 + 166.8x + 6196 R(10) = −4.1(10)2 + 166.8(10) + 6196 Using a calculator, we estimate: R(1) ≈ 7454 Hence, when the ﬁrm invests $10,000 in advertising, their revenue is approximately $7,454,000. 3. To ﬁnd the concentration of medication in the patient’s blood after 2 hours, locate the number 2 on the horizontal axis, draw a vertical arrow to the graph, then a horizontal arrow to the vertical axis. It appears that this last arrow points at a number slightly above 60 mg/L. We’ll guess 63 mg/L. Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 292 C (mg/L) 100 80 60 40 20 t (Hours) 0 0 1 2 3 To use the polynomial to ﬁnd the medication concentration after 2 hours, substitute 2 for t in the given polynomial. C(t) = −56.214t2 + 139.31t + 9.35 C(2) = −56.214(2)2 + 139.31(2) + 9.35 Using a calculator, we estimate: N (3) ≈ 63 Hence, the concentration of medication in the patient’s blood after 2 hours is approximately 63 mg/L. 5. The projectile’s height above ground is given by the formula 1 y = y0 + v0 t − gt2 , 2 where the initial height is 75 meters, the initial velocity is v0 = 457 meters per second, and the acceleration due to gravity is g = 9.8 meters per second per second. We’re asked to ﬁnd when the object ﬁrst reaches a height of y = 6592 meters. Substituting these numbers, the formula becomes 1 6592 = 75 + 457t − (9.8)t2 , 2 or equivalently, 6592 = 75 + 457t − 4.9t2 . Load each side of this equation into the Y= menu of your graphing calculator, then set the WINDOW parameters as follows: Xmin=0, Xmax=100, Ymin=0, Second Edition: 2012-2013 5.3. APPLICATIONS OF POLYNOMIALS 293 and Ymax=10800. Push the GRAPH button to produce the graph, then use the 5:intersect tool from the CALC menu to ﬁnd the ﬁrst time the height of the object reaches 6592 meters. Report the results on your homework as shown in the following graph. y 10,800 y = 75 + 457t − 4.9t2 y = 6592 0 0 17.6 100 t Hence, the projectile ﬁrst reaches a height of 6592 meters at approximately 17.6 seconds. 7. The projectile’s height above ground is given by the formula 1 y = y0 + v0 t − gt2 , 2 where the initial height is 58 meters, the initial velocity is v0 = 229 meters per second, and the acceleration due to gravity is g = 9.8 meters per second per second. We’re asked to ﬁnd when the object ﬁrst reaches a height of y = 1374 meters. Substituting these numbers, the formula becomes 1 1374 = 58 + 229t − (9.8)t2 , 2 or equivalently, 1374 = 58 + 229t − 4.9t2 . Load each side of this equation into the Y= menu of your graphing calculator, then set the WINDOW parameters as follows: Xmin=0, Xmax=50, Ymin=0, and Ymax=2800. Push the GRAPH button to produce the graph, then use the 5:intersect tool from the CALC menu to ﬁnd the ﬁrst time the height of the object reaches 1374 meters. Report the results on your homework as shown in the following graph. Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 294 y y = 58 + 229t − 4.9t2 2,800 y = 1374 0 0 6.7 50 t Hence, the projectile ﬁrst reaches a height of 1374 meters at approximately 6.7 seconds. 9. To ﬁnd the zero of f (x) = 3.25x − 4.875 algebraically, set f (x) = 0 and solve for x. f (x) = 0 3.25x − 4.875 = 0 We want the value of x that makes the function equal to zero. Replace f (x) with 3.25x − 4.875. Now, solve for x. 3.25x = 4.875 4.875 3.25x = 3.25 3.25 x = 1.5 Add 4.875 to both sides. Divide both sides by 3.25. Simplify. Hence, 1.5 is a zero of f (x) = 3.25x − 4.875. Next, load the function into the Y= menu, select 6:ZStandard from the ZOOM menu, then use the utility 2:zero from the CALC menu to ﬁnd the zero of the function. Second Edition: 2012-2013 5.3. APPLICATIONS OF POLYNOMIALS 295 Next, use the Calculator Submission Guidelines when crafting the following report on your homework paper. Draw a dashed vertical line through the xintercept and label it with its coordinates. y f 10 −10 (1.5, 0) 10 x −10 Note how the graphical solution agrees with the algebraic solution. 11. To ﬁnd the zero of f (x) = 3.9 − 1.5x algebraically, set f (x) = 0 and solve for x. f (x) = 0 3.9 − 1.5x = 0 We want the value of x that makes the function equal to zero. Replace f (x) with 3.9 − 1.5x. Now, solve for x. −1.5x = −3.9 −1.5x −3.9 = −1.5 −1.5 x = 2.6 Subtract 3.9 from both sides. Divide both sides by −1.5. Simplify. Hence, 2.6 is a zero of f (x) = 3.9 − 1.5x. Next, load the function into the Y= menu, select 6:ZStandard from the ZOOM menu, then use the utility 2:zero from the CALC menu to ﬁnd the zero of the function. Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 296 Next, use the Calculator Submission Guidelines when crafting the following report on your homework paper. Draw a dashed vertical line through the xintercept and label it with its coordinates. y f 10 (2.6, 0) −10 10 x −10 Note how the graphical solution agrees with the algebraic solution. 13. The projectile’s height above ground is given by the formula 1 y = y0 + v0 t − gt2 , 2 where the initial height is 52 meters, the initial velocity is v0 = 203 meters per second, and the acceleration due to gravity is g = 9.8 meters per second per Second Edition: 2012-2013 5.3. APPLICATIONS OF POLYNOMIALS 297 second. Substituting these numbers, the formula becomes 1 y = 52 + 203t − (9.8)t2 , 2 or equivalently, y = 52 + 203t − 4.9t2 . We’re asked to ﬁnd the time it takes the projectile to return to ground level. When this happens, its height y above ground level will equal zero. Substitute 0 for y in the last equation. 0 = 52 + 203t − 4.9t2 . Load the right-hand side of this equation into the Y= menu of your graphing calculator, then set the WINDOW parameters as follows: Xmin=0, Xmax=50, Ymin=0, and Ymax=2200. Push the GRAPH button to produce the graph, then use the 2:zero tool from the CALC menu to ﬁnd where the graph of f crosses the x-axis. Report the results on your homework as shown in the following graph. y(meters) y = 52 + 203t − 4.9t2 2,200 0 0 50 41.7 t(seconds) Hence, the projectile reaches ground level at approximately 41.7 seconds. 15. The projectile’s height above ground is given by the formula 1 y = y0 + v0 t − gt2 , 2 where the initial height is 52 meters, the initial velocity is v0 = 276 meters per second, and the acceleration due to gravity is g = 9.8 meters per second per second. Substituting these numbers, the formula becomes 1 y = 52 + 276t − (9.8)t2 , 2 or equivalently, y = 52 + 276t − 4.9t2 . Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 298 We’re asked to ﬁnd the time it takes the projectile to return to ground level. When this happens, its height y above ground level will equal zero. Substitute 0 for y in the last equation. 0 = 52 + 276t − 4.9t2 . Load the right-hand side of this equation into the Y= menu of your graphing calculator, then set the WINDOW parameters as follows: Xmin=0, Xmax=60, Ymin=0, and Ymax=4000. Push the GRAPH button to produce the graph, then use the 2:zero tool from the CALC menu to ﬁnd where the graph of f crosses the x-axis. Report the results on your homework as shown in the following graph. y(meters) 4,000 0 y = 52 + 276t − 4.9t2 0 56.5 60 t(seconds) Hence, the projectile reaches ground level at approximately 56.5 seconds. 5.4 Adding and Subtracting Polynomials 1. Let’s arrange our answer in descending powers of r by listing the highest powers of r ﬁrst, then the next highest, and so on. Use the commutative and associative properties to change the order and regroup. Then combine like terms. (−8r2 t + 7rt2 + 3t3 ) + (9r3 + 2rt2 + 4t3 ) = (9r3 ) + (−8r2 t) + (7rt2 + 2rt2 ) + (3t3 + 4t3 ) = 9r3 − 8r2 t + 9rt2 + 7t3 3. Let’s arrange our answer in descending powers of x by listing the highest powers of x ﬁrst, then the next highest, and so on. Use the commutative and associative properties to change the order and regroup. Then combine like terms. (7x2 − 6x − 9) + (8x2 + 10x + 9) = (7x2 + 8x2 ) + (−6x + 10x) + (−9 + 9) = 15x2 + 4x Second Edition: 2012-2013 5.4. ADDING AND SUBTRACTING POLYNOMIALS 299 5. Let’s arrange our answer in descending powers of r by listing the highest powers of r ﬁrst, then the next highest, and so on. Use the commutative and associative properties to change the order and regroup. Then combine like terms. (−2r2 + 7rs + 4s2 ) + (−9r2 + 7rs − 2s2 ) = (−2r2 − 9r2 ) + (7rs + 7rs) + (4s2 − 2s2 ) = −11r2 + 14rs + 2s2 7. Let’s arrange our answer in descending powers of y by listing the highest powers of y ﬁrst, then the next highest, and so on. Use the commutative and associative properties to change the order and regroup. Then combine like terms. (−8y 3 − 3y 2 z − 6z 3 ) + (−3y 3 + 7y 2 z − 9yz 2 ) = (−8y 3 − 3y 3 ) + (−3y 2 z + 7y 2 z) + (−9yz 2) + (−6z 3 ) = −11y 3 + 4y 2 z − 9yz 2 − 6z 3 9. Negating a polynomial is accomplished by reversing the sign of each term of the polynomial. Thus, −(5x2 − 4) = −5x2 + 4 11. Negating a polynomial is accomplished by reversing the sign of each term of the polynomial. Thus, −(9r3 − 4r2 t − 3rt2 + 4t3 ) = −9r3 + 4r2 t + 3rt2 − 4t3 13. Negating a polynomial is accomplished by reversing the sign of each term of the polynomial. Thus, −(−5x2 + 9xy + 6y 2 ) = 5x2 − 9xy − 6y 2 15. To arrange the answer in descending powers of u, place the highest power of u ﬁrst, then the next highest, and so on. First, distribute the minus sign, changing the sign of each term of the second polynomial. (−u3 − 4u2 w + 7w3 ) − (u2 w + uw2 + 3w3 ) = −u3 − 4u2 w + 7w3 − u2 w − uw2 − 3w3 Now use the commutative and associative properties to change the order and regroup. Combine like terms. = (−u3 ) + (−4u2 w − u2 w) + (−uw2 ) + (7w3 − 3w3 ) = −u3 − 5u2 w − uw2 + 4w3 Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 300 17. To arrange the answer in descending powers of y, place the highest power of y ﬁrst, then the next highest, and so on. First, distribute the minus sign, changing the sign of each term of the second polynomial. (2y 3 − 2y 2 z + 3z 3 ) − (−8y 3 + 5yz 2 − 3z 3 ) = 2y 3 − 2y 2 z + 3z 3 + 8y 3 − 5yz 2 + 3z 3 Now use the commutative and associative properties to change the order and regroup. Combine like terms. = (2y 3 + 8y 3 ) + (−2y 2 z) + (−5yz 2) + (3z 3 + 3z 3 ) = 10y 3 − 2y 2 z − 5yz 2 + 6z 3 19. To arrange the answer in descending powers of r, place the highest power of r ﬁrst, then the next highest, and so on. First, distribute the minus sign, changing the sign of each term of the second polynomial. (−7r2 − 9rs − 2s2 ) − (−8r2 − 7rs + 9s2 ) = −7r2 − 9rs − 2s2 + 8r2 + 7rs − 9s2 Now use the commutative and associative properties to change the order and regroup. Combine like terms. = (−7r2 + 8r2 ) + (−9rs + 7rs) + (−2s2 − 9s2 ) = r2 − 2rs − 11s2 21. To arrange the answer in descending powers of x, place the highest power of x ﬁrst, then the next highest, and so on. First, distribute the minus sign, changing the sign of each term of the second polynomial. (10x2 + 2x − 6) − (−8x2 + 14x + 17) = 10x2 + 2x − 6 + 8x2 − 14x − 17 Now use the commutative and associative properties to change the order and regroup. Combine like terms. = (10x2 + 8x2 ) + (2x − 14x) + (−6 − 17) = 18x2 − 12x − 23 Second Edition: 2012-2013 5.4. ADDING AND SUBTRACTING POLYNOMIALS 301 23. To arrange our answer in descending powers of x, we need to ﬁrst list the highest power of x, then the next highest power, and so on. Use the commutative and associative properties to change the order and regroup. Then combine like terms. f (x) + g(x) = (−2x2 + 9x + 7) + (8x3 − 7x2 + 5) = (8x3 ) + (−2x2 − 7x2 ) + (9x) + (7 + 5) = 8x3 − 9x2 + 9x + 12 25. To arrange our answer in descending powers of x, we need to ﬁrst list the highest power of x, then the next highest power, and so on. Use the commutative and associative properties to change the order and regroup. Then combine like terms. f (x) + g(x) = (5x3 − 5x2 + 8x) + (7x2 − 2x − 9) = (5x3 ) + (−5x2 + 7x2 ) + (8x − 2x) + (−9) = 5x3 + 2x2 + 6x − 9 27. To arrange our answer in descending powers of x, we need to ﬁrst list the highest power of x, then the next highest power, and so on. Use the commutative and associative properties to change the order and regroup. Then combine like terms. f (x) + g(x) = (−3x2 − 8x − 9) + (5x2 − 4x + 4) = (−3x2 + 5x2 ) + (−8x − 4x) + (−9 + 4) = 2x2 − 12x − 5 29. To arrange our answer in descending powers of x, we need to ﬁrst list the highest power of x, then the next highest power, and so on. Use the commutative and associative properties to change the order and regroup. Then combine like terms. f (x) − g(x) = (−6x3 − 7x + 7) − (−3x3 − 3x2 − 8x) = −6x3 − 7x + 7 + 3x3 + 3x2 + 8x = (−6x3 + 3x3 ) + (3x2 ) + (−7x + 8x) + (7) = −3x3 + 3x2 + x + 7 Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 302 31. To arrange the answer in descending powers of x, place the highest power of x ﬁrst, then the next highest, and so on. First, distribute the minus sign, changing the sign of each term of the second polynomial. f (x) − g(x) = (12x2 − 5x + 4) − (8x2 − 16x − 7) = 12x2 − 5x + 4 − 8x2 + 16x + 7 Now use the commutative and associative properties to change the order and regroup. Combine like terms. = (12x2 − 8x2 ) + (−5x + 16x) + (4 + 7) = 4x2 + 11x + 11 33. To arrange our answer in descending powers of x, we need to ﬁrst list the highest power of x, then the next highest power, and so on. Use the commutative and associative properties to change the order and regroup. Then combine like terms. f (x) − g(x) = (−3x3 − 4x + 2) − (−4x3 − 7x2 + 6) = −3x3 − 4x + 2 + 4x3 + 7x2 − 6 = (−3x3 + 4x3 ) + (7x2 ) + (−4x) + (2 − 6) = x3 + 7x2 − 4x − 4 35. The two shaded squares in have areas A1 = x2 and A3 = 25, respectively. The two unshaded rectangles have areas A2 = 5x and A4 = 5x. x 5 5 A2 = 5x A3 = 25 5 x A1 = x2 A4 = 5x x x 5 Summing these four areas gives us the area of the entire ﬁgure. A = A1 + A2 + A3 + A4 = x2 + 5x + 25 + 5x = x2 + 10x + 25 Second Edition: 2012-2013 5.5. LAWS OF EXPONENTS 303 37. The proﬁt made from selling x wicker baskets is found by subtracting the costs incurred from the revenue received. In symbols: P (x) = R(x) − C(x) Next, replace R(x) and C(x) with their deﬁnitions. Because we are supposed to subtract all of the cost from the revenue, be sure to surround the cost polynomial with parentheses. P (x) = 33.45x − (232 + 7x − 0.0085x2) Distribute the minus sign and combine like terms. = 33.45x − 232 − 7x + 0.0085x2 = −232 + 26.45x + 0.0085x2 Thus, the proﬁt function is P (x) = −232 + 26.45x + 0.0085x2. Next, to determine the proﬁt if 233 wicker baskets are sold, subsitute 233 for x in the proﬁt function P (x). P (x) = −232 + 26.45x + 0.0085x2 P (233) = −232 + 26.45(233) + 0.0085(233)2 You can now use your graphing calculator to determine the proﬁt. P (233) = 6392.3065 Rounding to the nearest cent, the proﬁt is $6,392.31. 5.5 Laws of Exponents 1. The exponent tells us how many times to write the base as a factor. (−4)3 = (−4)(−4)(−4) = −64 Write −4 as a factor 3 times. Multiply. 3. If you raise any number (other than zero) to the zero power, the answer is 1. 0 5 =1 − 7 Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 304 5. The exponent tells us how many times to write the base as a factor. 2 4 4 4 − = − − Write −4/3 as a factor 2 times. 3 3 3 16 Multiply. = 9 7. If you raise any number (other than zero) to the zero power, the answer is 1. (−19)0 = 1 9. When multiplying like bases, use the law am an = am+n . That is, repeat the base and add the exponents. (7v − 6w)18 · (7v − 6w)17 = (7v − 6w)18+17 35 = (7v − 6w) Repeat the base, add the exponents. Simplify: 18 + 17 = 35 11. When multiplying like bases, use the law am an = am+n . That is, repeat the base and add the exponents. 34 · 30 = 34+0 =3 4 Repeat the base, add the exponents. Simplify: 4 + 0 = 4 If you wish, you can use your calculator to compute 34 = 81. However, reporting the answer in exponential form 34 is far easier. 13. When multiplying like bases, use the law am an = am+n . That is, repeat the base and add the exponents. 4n · 48n+3 = 4(n)+(8n+3) =4 =4 (n+8n)+(3) 9n+3 Repeat the base, add the exponents. Group like terms. Simplify. 15. When multiplying like bases, use the law am an = am+n . That is, repeat the base and add the exponents. x8 · x3 = x8+3 11 =x Second Edition: 2012-2013 Repeat the base, add the exponents. Simplify: 8 + 3 = 11 5.5. LAWS OF EXPONENTS 305 17. When multiplying like bases, use the law am an = am+n . That is, repeat the base and add the exponents. 25 · 23 = 25+3 =2 Repeat the base, add the exponents. 8 Simplify: 5 + 3 = 8 If you wish, you can use your calculator to compute 28 = 256. However, reporting the answer in exponential form 28 is far easier. 19. When dividing like bases, use the law am /an = am−n . That is, repeat the base and subtract the exponents. 416 = 416−16 416 = 40 =1 Repeat the base, subtract the exponents. Simplify: 16 − 16 = 0 Any number (except zero) to the zero power equals 1. Hence, 416 /416 = 1. 21. When dividing like bases, use the law am /an = am−n . That is, repeat the base and subtract the exponents. w11 = w11−7 w7 = w4 Repeat the base, subtract the exponents. Simplify: 11 − 7 = 4 23. When dividing like bases, use the law am /an = am−n . That is, repeat the base and subtract the exponents. (9a − 8c)15 = (9a − 8c)15−8 (9a − 8c)8 = (9a − 8c)7 Repeat the base, subtract the exponents. Simplify: 15 − 8 = 7 25. When dividing like bases, use the law am /an = am−n . That is, repeat the base and subtract the exponents. 29n+5 = 2(9n+5)−(3n−4) 23n−4 = 29n+5−3n+4 =2 =2 (9n−3n)+(5+4) 6n+9 Repeat the base, subtract the exponents. Distribute minus sign. Group like terms. Simplify. Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 306 27. When dividing like bases, use the law am /an = am−n . That is, repeat the base and subtract the exponents. 417 = 417−9 49 = 48 Repeat the base, subtract the exponents. Simplify: 17 − 9 = 8 If you wish, you can use your calculator to compute 48 = 65536. However, reporting the answer in exponential form 48 is far easier. 29. When raising a power to a power, use the law (am )n = amn . That is, repeat the base and multiply the exponents. 8m−6 7 4 = 47(8m−6) =4 Repeat the base, multiply the exponents. 56m−42 Distribute 7. 31. When raising a power to a power, use the law (am )n = amn . That is, repeat the base and multiply the exponents. 7 (9x + 5y)3 = (9x + 5y)(3)(7) 21 = (9x + 5y) Repeat the base, multiply the exponents. Simplify: (3)(7) = 21 33. When raising a power to a power, use the law (am )n = amn . That is, repeat the base and multiply the exponents. 3 2 4 = 4(3)(2) =4 6 Repeat the base, multiply the exponents. Simplify: (3)(2) = 6 If you wish, you can use your calculator to compute 46 = 4096. However, reporting the answer in exponential form 46 is far easier. 35. When raising a power to a power, use the law (am )n = amn . That is, repeat the base and multiply the exponents. 4 7 c = c(4)(7) =c 28 Second Edition: 2012-2013 Repeat the base, multiply the exponents. Simplify: (4)(7) = 28 5.5. LAWS OF EXPONENTS 307 37. When raising a power to a power, use the law (am )n = amn . That is, repeat the base and multiply the exponents. 2 0 6 = 6(2)(0) Repeat the base, multiply the exponents. = 60 =1 Simplify: (2)(0) = 0 Any number (except zero) raised to the zero power is 1. 0 Hence, 62 = 1. 39. When raising a product to a power, use the law (ab)n = an bn . That is, raise each factor to the n. (uw)5 = u5 w5 Raise each factor to the 5. 41. When raising a product to a power, use the law (ab)n = an bn . That is, raise each factor to the n. (−2y)3 = (−2)3 (y)3 = −8y 3 Raise each factor to the 3. Simplify: (−2)3 = −8 43. When raising a product to a power, use the law (ab)n = an bn . That is, raise each factor to the n. (3w9 )4 = (3)4 (w9 )4 = 81w 36 Raise each factor to the 4. Simplify: (3)4 = 81 and (w9 )4 = w36 45. When raising a product to a power, use the law (ab)n = an bn . That is, raise each factor to the n. (−3x8 y 2 )4 = (−3)4 (x8 )4 (y 2 )4 32 8 = 81x y Raise each factor to the 4. Simplify: (−3)4 = 81, (x8 )4 = x32 , and (y 2 )4 = y 8 47. When raising a product to a power, use the law (ab)n = an bn . That is, raise each factor to the n. (7s6n )3 = (7)3 (s6n )3 = 343s 18n Raise each factor to the 3. Simplify: (7)3 = 343, (s6n )3 = s18n Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 308 49. When raising a quotient to a power, use the law (a/b)n = an /bn . That is, raise both numerator and denominator to the n. v 3 v 3 = 3 Raise numerator and denominator 2 2 to the third power. = v3 8 Simplify: (2)3 = 8 51. When raising a quotient to a power, use the law (a/b)n = an /bn . That is, raise both numerator and denominator to the n. When you raise a negative fraction to an even power, the answer is positive. 2 22 2 = 2 Raise numerator and denominator − u u to the second power. 4 Simplify: (2)2 = 4 = 2 u 53. When raising a quotient to a power, use the law (a/b)n = an /bn . That is, raise both numerator and denominator to the n. When you raise a negative fraction to an even power, the answer is positive. 8 4 8 4 r r = Raise numerator and denominator − 5 54 to the fourth power. 4 r32 = Simplify: r8 = r32 and (5)4 = 625 625 55. When raising a quotient to a power, use the law (a/b)n = an /bn . That is, raise both numerator and denominator to the n. 4 54 5 = Raise numerator and denominator 4 c9 (c9 ) to the fourth power. 4 625 Simplify: (5)4 = 625 and c9 = c36 = 36 c 57. When raising a quotient to a power, use the law (a/b)n = an /bn . That is, raise both numerator and denominator to the n. 2 5 52 = Raise numerator and denominator 12 u (u12 )2 to the second power. 2 25 = 24 Simplify: (5)2 = 25 and u12 = u24 u Second Edition: 2012-2013 5.6. MULTIPLYING POLYNOMIALS 5.6 309 Multiplying Polynomials 1. Use the commutative and associative properties to change the order and regroup. −3(7r) = [(−3)(7)]r = −21r Reorder. Regroup. Multiply: (−3)(7) = −21 3. Use the commutative and associative properties to change the order and regroup. (−9b3 )(−8b6 ) = [(−9)(−8)](b3 b6 ) = 72b 9 Reorder. Regroup. Multiply: (−9)(−8) = 72, b3 b6 = b9 . 5. Use the commutative and associative properties to change the order and regroup. (−7r2 t4 )(7r5 t2 ) = [(−7)(7)](r2 r5 )(t4 t2 ) 7 6 Reorder. Regroup. Multiply: (−7)(7) = −49, r2 r5 = r7 , = −49r t and t4 t2 = t6 7. Use the commutative and associative properties to change the order and regroup. (−5b2 c9 )(−8b4 c4 ) = [(−5)(−8)](b2 b4 )(c9 c4 ) 6 13 Reorder. Regroup. Multiply: (−5)(−8) = 40, b2 b4 = b6 , = 40b c and c9 c4 = c13 9. Use the commutative and associative properties to change the order and regroup. (−8v 3 )(4v 4 ) = [(−8)(4)](v 3 v 4 ) = −32v 7 Reorder. Regroup. Multiply: (−8)(4) = −32, v 3 v 4 = v 7 . Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 310 11. We need to ﬁrst distribute the 9 times each term of the polynomial. Then we multiply the resulting monomials mentally. 9(−2b2 + 2b + 9) = 9(−2b2 ) + 9(2b) + 9(9) = −18b2 + 18b + 81 Alternate solution. Note that it is more eﬃcient to distribute 9 times each term of −2b2 + 2b + 9, performing the calculations mentally as you go. 9(−2b2 + 2b + 9) = −18b2 + 18b + 81 13. We need to ﬁrst distribute the −4 times each term of the polynomial. Then we multiply the resulting monomials mentally. −4(10t2 − 7t − 6) = −4(10t2 ) − (−4)(7t) − (−4)(6) = −40t2 − (−28t) − (−24) = −40t2 + 28t + 24 Alternate solution. Note that it is more eﬃcient to distribute −4 times each term of 10t2 − 7t − 6, performing the calculations mentally as you go. −4(10t2 − 7t − 6) = −40t2 + 28t + 24 15. We need to ﬁrst distribute the −8u2 times each term of the polynomial. Then we multiply the resulting monomials mentally. − 8u2 (−7u3 − 8u2 − 2u + 10) = −8u2 (−7u3 ) − (−8u2 )(8u2 ) − (−8u2 )(2u) + (−8u2 )(10) = 56u5 − (−64u4 ) − (−16u3) + (−80u2 ) = 56u5 + 64u4 + 16u3 − 80u2 Alternate solution. Note that it is more eﬃcient to distribute −8u2 times each term of −7u3 − 8u2 − 2u + 10, performing the calculations mentally as you go. −8u2 (−7u3 − 8u2 − 2u + 10) = 56u5 + 64u4 + 16u3 − 80u2 17. We need to ﬁrst distribute the 10s2 times each term of the polynomial. Then we multiply the resulting monomials mentally. 10s2 (−10s3 + 2s2 + 2s + 8) = 10s2 (−10s3 ) + 10s2 (2s2 ) + 10s2 (2s) + 10s2 (8) = −100s5 + 20s4 + 20s3 + 80s2 Alternate solution. Note that it is more eﬃcient to distribute 10s2 times each term of −10s3 + 2s2 + 2s + 8, performing the calculations mentally as you go. 10s2 (−10s3 + 2s2 + 2s + 8) = −100s5 + 20s4 + 20s3 + 80s2 Second Edition: 2012-2013 5.6. MULTIPLYING POLYNOMIALS 311 19. We need to ﬁrst distribute the 2st times each term of the polynomial. Then we multiply the resulting monomials mentally. 2st(−4s2 + 8st − 10t2 ) = 2st(−4s2 ) + 2st(8st) − 2st(10t2 ) = −8s3 t + 16s2 t2 − 20st3 Alternate solution. Note that it is more eﬃcient to distribute 2 times each term of −4s2 + 8st − 10t2 , performing the calculations mentally as you go. 2st(−4s2 + 8st − 10t2 ) = −8s3 t + 16s2 t2 − 20st3 21. We need to ﬁrst distribute the −2uw times each term of the polynomial. Then we multiply the resulting monomials mentally. −2uw(10u2 − 7uw − 2w2 ) = −2uw(10u2) − (−2uw)(7uw) − (−2uw)(2w2 ) = −20u3w − (−14u2 w2 ) − (−4uw3 ) = −20u3w + 14u2 w2 + 4uw3 Alternate solution. Note that it is more eﬃcient to distribute −2 times each term of 10u2 − 7uw − 2w2 , performing the calculations mentally as you go. −2uw(10u2 − 7uw − 2w2 ) = −20u3w + 14u2w2 + 4uw3 23. Let’s imagine that (−9x − 4)(−3x + 2) has the form (b + c)a and multiply −3x + 2 times both terms of −9x − 4. (−9x − 4)(−3x + 2) = −9x(−3x + 2) − 4(−3x + 2) Now we distribute monomials times polynomials, then combine like terms. = 27x2 − 18x + 12x − 8 = 27x2 − 6x − 8 Thus, (−9x − 4)(−3x + 2) = 27x2 − 6x − 8 25. Let’s imagine that (3x + 8)(3x − 2) has the form (b + c)a and multiply 3x − 2 times both terms of 3x + 8. (3x + 8)(3x − 2) = 3x(3x − 2) + 8(3x − 2) Now we distribute monomials times polynomials, then combine like terms. = 9x2 − 6x + 24x − 16 = 9x2 + 18x − 16 Thus, (3x + 8)(3x − 2) = 9x2 + 18x − 16 Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 312 27. Let’s imagine that (2x − 1)(−6x2 + 4x + 5) has the form (b + c)a and multiply −6x2 + 4x + 5 times both terms of 2x − 1. (2x − 1)(−6x2 + 4x + 5) = 2x(−6x2 + 4x + 5) − 1(−6x2 + 4x + 5) Now we distribute monomials times polynomials, then combine like terms. = −12x3 + 8x2 + 10x + 6x2 − 4x − 5 = −12x3 + 14x2 + 6x − 5 Thus, (2x − 1)(−6x2 + 4x + 5) = −12x3 + 14x2 + 6x − 5 29. Let’s imagine that (x−6)(−2x2 −4x−4) has the form (b+c)a and multiply −2x2 − 4x − 4 times both terms of x − 6. (x − 6)(−2x2 − 4x − 4) = x(−2x2 − 4x − 4) − 6(−2x2 − 4x − 4) Now we distribute monomials times polynomials, then combine like terms. = −2x3 − 4x2 − 4x + 12x2 + 24x + 24 = −2x3 + 8x2 + 20x + 24 Thus, (x − 6)(−2x2 − 4x − 4) = −2x3 + 8x2 + 20x + 24 31. First, multiply 8u times each term of 8u − 9w, then multiply −9w times each term of 8u − 9w. Finally, combine like terms. (8u − 9w)(8u − 9w) = 8u(8u − 9w) − 9w(8u − 9w) = 64u2 − 72uw − 72uw + 81w2 = 64u2 − 144uw + 81w2 Thus, (8u − 9w)(8u − 9w) = 64u2 − 144uw + 81w2 . 33. First, multiply 9r times each term of 3r − 9t, then multiply −7t times each term of 3r − 9t. Finally, combine like terms. (9r − 7t)(3r − 9t) = 9r(3r − 9t) − 7t(3r − 9t) = 27r2 − 81rt − 21rt + 63t2 = 27r2 − 102rt + 63t2 Thus, (9r − 7t)(3r − 9t) = 27r2 − 102rt + 63t2 . Second Edition: 2012-2013 5.6. MULTIPLYING POLYNOMIALS 313 35. First, multiply 4r times each term of −10r2 + 10rs − 7s2 , then multiply −10s times each term of −10r2 + 10rs − 7s2 . Finally, combine like terms. (4r − 10s)(−10r2 + 10rs − 7s2 ) = 4r(−10r2 + 10rs − 7s2 ) − 10s(−10r2 + 10rs − 7s2 ) = −40r3 + 40r2 s − 28rs2 + 100r2 s − 100rs2 + 70s3 = −40r3 + 140r2 s − 128rs2 + 70s3 Thus, (4r − 10s)(−10r2 + 10rs − 7s2 ) = −40r3 + 140r2 s − 128rs2 + 70s3 . 37. First, multiply 9x times each term of 4x2 − 4xz − 10z 2, then multiply −2z times each term of 4x2 − 4xz − 10z 2 . Finally, combine like terms. (9x − 2z)(4x2 − 4xz − 10z 2 ) = 9x(4x2 − 4xz − 10z 2 ) − 2z(4x2 − 4xz − 10z 2) = 36x3 − 36x2 z − 90xz 2 − 8x2 z + 8xz 2 + 20z 3 = 36x3 − 44x2 z − 82xz 2 + 20z 3 Thus, (9x − 2z)(4x2 − 4xz − 10z 2 ) = 36x3 − 44x2 z − 82xz 2 + 20z 3. 39. First, write 9r + 3t as a factor two times. (9r + 3t)2 = (9r + 3t)(9r + 3t) Next, multiply 9r times each term of 9r + 3t, then multiply 3t times each term of 9r + 3t. Finally, combine like terms. = 9r(9r + 3t) + 3t(9r + 3t) = 81r2 + 27rt + 27rt + 9t2 = 81r2 + 54rt + 9t2 Thus, (9r + 3t)2 = 81r2 + 54rt + 9t2 . 41. First, multiply 4y times each term of 4y − 5z, then multiply 5z times each term of 4y − 5z. Finally, combine like terms. (4y + 5z)(4y − 5z) = 4y(4y − 5z) + 5z(4y − 5z) = 16y 2 − 20yz + 20yz − 25z 2 = 16y 2 − 25z 2 Thus, (4y + 5z)(4y − 5z) = 16y 2 − 25z 2. Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 314 43. First, multiply 7u times each term of 7u − 8v, then multiply 8v times each term of 7u − 8v. Finally, combine like terms. (7u + 8v)(7u − 8v) = 7u(7u − 8v) + 8v(7u − 8v) = 49u2 − 56uv + 56uv − 64v 2 = 49u2 − 64v 2 Thus, (7u + 8v)(7u − 8v) = 49u2 − 64v 2 . 45. First, write 7b + 8c as a factor two times. (7b + 8c)2 = (7b + 8c)(7b + 8c) Next, multiply 7b times each term of 7b + 8c, then multiply 8c times each term of 7b + 8c. Finally, combine like terms. = 7b(7b + 8c) + 8c(7b + 8c) = 49b2 + 56bc + 56bc + 64c2 = 49b2 + 112bc + 64c2 Thus, (7b + 8c)2 = 49b2 + 112bc + 64c2 . 47. Multiply 2t2 times each term of 2t2 + 9t + 4, multiply 9t times each term of 2t2 + 9t + 4, and multiply 4 times each term of 2t2 + 9t + 4. Finally, combine like terms. (2t2 + 9t + 4)(2t2 + 9t + 4) = 2t2 (2t2 + 9t + 4) + 9t(2t2 + 9t + 4) + 4(2t2 + 9t + 4) = 4t4 + 18t3 + 8t2 + 18t3 + 81t2 + 36t + 8t2 + 36t + 16 = 4t4 + 36t3 + 97t2 + 72t + 16 Thus, (2t2 + 9t + 4)(2t2 + 9t + 4) = 4t4 + 36t3 + 97t2 + 72t + 16. 49. Multiply 4w2 times each term of 3w2 − 6w + 8, multiply 3w times each term of 3w2 − 6w + 8, and multiply 5 times each term of 3w2 − 6w + 8. Finally, combine like terms. (4w2 + 3w + 5)(3w2 − 6w + 8) = 4w2 (3w2 − 6w + 8) + 3w(3w2 − 6w + 8) + 5(3w2 − 6w + 8) = 12w4 − 24w3 + 32w2 + 9w3 − 18w2 + 24w + 15w2 − 30w + 40 = 12w4 − 15w3 + 29w2 − 6w + 40 Thus, (4w2 + 3w + 5)(3w2 − 6w + 8) = 12w4 − 15w3 + 29w2 − 6w + 40. Second Edition: 2012-2013 5.6. MULTIPLYING POLYNOMIALS 315 51. To ﬁnd the revenue, we must multiply the number of widgets sold by the price for each widget. That is, we must multiply the demand times the unit price. Revenue = Demand × Unit Price Let R represent the revenue. Because x represents the demand and p represents the unit price, the last equation can be rewritten as follows. R = xp However, the demand is given by the equation x = 320 − 0.95p. Substitute 320 − 0.95p for x in the last equation to get R = (320 − 0.95p)p, or equivalently, R = 320p − 0.95p2 . We’re asked to ﬁnd when the revenue equals R = 7, 804, so enter Y 1 = 320 ∗ X − 0.95 ∗ X ∧ 2 and Y 2 = 7804 into the Y= menu in your calculator, then set the WINDOW parameters as follows: Xmin=0, Xmax=350, Ymin=0, Ymax=27000. Push the GRAPH button to produce the graph, then use the 5:intersect utility to determine the coordinates of the points of intersection. Report your answer on your homework as follows. R(dollars) 27,000 R = 320p − 0.95p2 R = 7804 0 026.47 310.37350 p(dollars) Hence, the revenue will equal R = $7, 804 if the unit price is set either at $26.47 or $310.37. 53. Because the edge of the outer square is 6 inches longer that 3 times the edge of the inner square, the edge of the outer square is 3x + 6. x 3x + 6 Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 316 To ﬁnd the area of the shaded region, subtract the area of the smaller square from the area of the larger square. Recall that the area of a square is found by squaring the length of one of its sides. Area of shaded region = Area of larger square − Area of smaller square A(x) = (3x + 6)2 − x2 Use the distributive property to multiply. A(x) = (3x + 6)(3x + 6) − x2 A(x) = 9x2 + 18x + 18x + 36 − x2 Combine like terms. A(x) = 8x2 + 36x + 36 Hence, the area of the shaded region is given by the polynomial A(x) = 8x2 + 36x + 36. We can now evaluate the polynomial at x = 5 inches by substituting 5 for x. A(x) = 8x2 + 36x + 36 A(5) = 8(5)2 + 36(5) + 36 Use your calculator to help simplify. A(5) = 416 Hence, the area of the shaded region is 416 square inches. 55. If the width of the entire rectangular garden is 29 feet, and the width of the border lawn is x feet, then the width of the interior rectangular garden is 29 − 2x feet. Simlarly, if the length of the entire rectangular garden is 31 feet, and the width of the border lawn is x feet, then the length of the interior rectangular garden is 31 − 2x feet. 29 − 2x x 29 x x 31 − 2x x 31 Second Edition: 2012-2013 5.7. SPECIAL PRODUCTS 317 Therefore, the dimensions of the inner rectangular garden are 31 − 2x by 29 − 2x feet. Thus, the area of the inner rectangular garden is: A(x) = (31 − 2x)(29 − 2x) We are required to express our answer in the standard form A(x) = ax2 +bx+c, so we use the distributive property to multiply. A(x) = 899 − 62x − 58x + 4x2 A(x) = 899 − 120x + 4x2 Now, if the uniform width of the lawn border is 9.3 feet, substitute 9.3 for x in the polynomial that gives the area of the inner rectangular garden. A(x) = 899 − 120x + 4x2 A(9.3) = 899 − 120(9.3) + 4(9.3)2 Use a calculator to compute the answer. A(9.3) = 128.96 Hence, the area of the inner rectangular garden is 128.96 square feet. 5.7 Special Products 1. Each of the following steps is performed mentally. i) Multiply the terms in the “First” positions: (5x)(3x) = 15x2 ii) Multiply the terms in the “Outer” and “Inner” positions and add the results mentally: 20x + 6x = 26x iii) Multiply the terms in the “Last” positions: (2)(4) = 8 Write the answer with no intermediate steps: (5x + 2)(3x + 4) = 15x2 + 26x + 8 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (5x + 2)(3x + 4) = 15x2 + 26x + 8 Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 318 3. Each of the following steps is performed mentally. i) Multiply the terms in the “First” positions: (6x)(5x) = 30x2 ii) Multiply the terms in the “Outer” and “Inner” positions and add the results mentally: 24x − 15x = 9x iii) Multiply the terms in the “Last” positions: (−3)(4) = −12 Write the answer with no intermediate steps: (6x − 3)(5x + 4) = 30x2 + 9x − 12 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (6x − 3)(5x + 4) = 30x2 + 9x − 12 5. Each of the following steps is performed mentally. i) Multiply the terms in the “First” positions: (5x)(3x) = 15x2 ii) Multiply the terms in the “Outer” and “Inner” positions and add the results mentally: −20x − 18x = −38x iii) Multiply the terms in the “Last” positions: (−6)(−4) = 24 Write the answer with no intermediate steps: (5x − 6)(3x − 4) = 15x2 − 38x + 24 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (5x − 6)(3x − 4) = 15x2 − 38x + 24 7. Each of the following steps is performed mentally. i) Multiply the terms in the “First” positions: (6x)(3x) = 18x2 ii) Multiply the terms in the “Outer” and “Inner” positions and add the results mentally: −30x − 6x = −36x iii) Multiply the terms in the “Last” positions: (−2)(−5) = 10 Write the answer with no intermediate steps: (6x − 2)(3x − 5) = 18x2 − 36x + 10 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (6x − 2)(3x − 5) = 18x2 − 36x + 10 Second Edition: 2012-2013 5.7. SPECIAL PRODUCTS 319 9. Each of the following steps is performed mentally. i) Multiply the terms in the “First” positions: (6x)(3x) = 18x2 ii) Multiply the terms in the “Outer” and “Inner” positions and add the results mentally: 30x + 12x = 42x iii) Multiply the terms in the “Last” positions: (4)(5) = 20 Write the answer with no intermediate steps: (6x + 4)(3x + 5) = 18x2 + 42x + 20 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (6x + 4)(3x + 5) = 18x2 + 42x + 20 11. Each of the following steps is performed mentally. i) Multiply the terms in the “First” positions: (4x)(6x) = 24x2 ii) Multiply the terms in the “Outer” and “Inner” positions and add the results mentally: 12x − 30x = −18x iii) Multiply the terms in the “Last” positions: (−5)(3) = −15 Write the answer with no intermediate steps: (4x − 5)(6x + 3) = 24x2 − 18x − 15 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (4x − 5)(6x + 3) = 24x2 − 18x − 15 13. Note how the terms in the “First” position are identical, as are the terms in the “Last” position, with one set separated by a plus sign and the other with a minus sign. Hence, this is the diﬀerence of squares pattern and we proceed as follows: i) Square the term in the “First” position: (10x)2 = 100x2 ii) Square the term in the “Last” position: (12)2 = 144 iii) Separate the squares with a minus sign. Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 320 That is: (10x − 12)(10x + 12) = (10x)2 − (12)2 = 100x2 − 144 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (10x − 12)(10x + 12) = 100x2 − 144 15. Note how the terms in the “First” position are identical, as are the terms in the “Last” position, with one set separated by a plus sign and the other with a minus sign. Hence, this is the diﬀerence of squares pattern and we proceed as follows: i) Square the term in the “First” position: (6x)2 = 36x2 ii) Square the term in the “Last” position: (9)2 = 81 iii) Separate the squares with a minus sign. That is: (6x + 9)(6x − 9) = (6x)2 − (9)2 = 36x2 − 81 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (6x + 9)(6x − 9) = 36x2 − 81 17. Note how the terms in the “First” position are identical, as are the terms in the “Last” position, with one set separated by a plus sign and the other with a minus sign. Hence, this is the diﬀerence of squares pattern and we proceed as follows: i) Square the term in the “First” position: (3x)2 = 9x2 ii) Square the term in the “Last” position: (10)2 = 100 iii) Separate the squares with a minus sign. That is: (3x + 10)(3x − 10) = (3x)2 − (10)2 = 9x2 − 100 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (3x + 10)(3x − 10) = 9x2 − 100 Second Edition: 2012-2013 5.7. SPECIAL PRODUCTS 321 19. Note how the terms in the “First” position are identical, as are the terms in the “Last” position, with one set separated by a plus sign and the other with a minus sign. Hence, this is the diﬀerence of squares pattern and we proceed as follows: i) Square the term in the “First” position: (10x)2 = 100x2 ii) Square the term in the “Last” position: (9)2 = 81 iii) Separate the squares with a minus sign. That is: (10x − 9)(10x + 9) = (10x)2 − (9)2 = 100x2 − 81 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (10x − 9)(10x + 9) = 100x2 − 81 21. Follow these steps: i) Square the ﬁrst term: (2x)2 = 4x2 ii) Multiply the “First” and “Last” terms and double the result: 2(2x)(3) = 12x iii) Square the “Last” term: (3)2 = 9 Thus: (2x + 3)2 = (2x)2 + 2(2x)(3) + (3)2 = 4x2 + 12x + 9 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (2x + 3)2 = 4x2 + 12x + 9 23. You can start by writing the diﬀerence as a sum: (9x − 8)2 = (9x + (−8))2 Follow these steps: i) Square the ﬁrst term: (9x)2 = 81x2 Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 322 ii) Multiply the “First” and “Last” terms and double the result: 2(9x)(−8) = −144x iii) Square the “Last” term: (−8)2 = 64 Thus: (9x − 8)2 = (9x + (−8))2 = (9x)2 + 2(9x)(−8) + (−8)2 = 81x2 − 144x + 64 Alternately, you can note that (a − b)2 = a2 − 2ab + b2 , so when the terms of the binomial are separated by a minus sign, the middle term of the result will also be minus. This allows us to move more quickly, writing: (9x − 8)2 = (9x)2 − 2(9x)(8) + (8)2 = 81x2 − 144x + 64 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in (9x − 8)2 = 81x2 − 144x + 64. 25. Follow these steps: i) Square the ﬁrst term: (7x)2 = 49x2 ii) Multiply the “First” and “Last” terms and double the result: 2(7x)(2) = 28x iii) Square the “Last” term: (2)2 = 4 Thus: (7x + 2)2 = (7x)2 + 2(7x)(2) + (2)2 = 49x2 + 28x + 4 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (7x + 2)2 = 49x2 + 28x + 4 27. You can start by writing the diﬀerence as a sum: (6x − 5)2 = (6x + (−5))2 Follow these steps: Second Edition: 2012-2013 5.7. SPECIAL PRODUCTS 323 i) Square the ﬁrst term: (6x)2 = 36x2 ii) Multiply the “First” and “Last” terms and double the result: 2(6x)(−5) = −60x iii) Square the “Last” term: (−5)2 = 25 Thus: (6x − 5)2 = (6x + (−5))2 = (6x)2 + 2(6x)(−5) + (−5)2 = 36x2 − 60x + 25 Alternately, you can note that (a − b)2 = a2 − 2ab + b2 , so when the terms of the binomial are separated by a minus sign, the middle term of the result will also be minus. This allows us to move more quickly, writing: (6x − 5)2 = (6x)2 − 2(6x)(5) + (5)2 = 36x2 − 60x + 25 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in (6x − 5)2 = 36x2 − 60x + 25. 29. Note how the terms in the “First” position are identical, as are the terms in the “Last” position, with one set separated by a plus sign and the other with a minus sign. Hence, this is the diﬀerence of squares pattern and we proceed as follows: i) Square the term in the “First” position: (11x)2 = 121x2 ii) Square the term in the “Last” position: (2)2 = 4 iii) Separate the squares with a minus sign. That is: (11x − 2)(11x + 2) = (11x)2 − (2)2 = 121x2 − 4 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (11x − 2)(11x + 2) = 121x2 − 4 Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 324 31. Follow these steps: i) Square the ﬁrst term: (7r)2 = 49r2 ii) Multiply the “First” and “Last” terms and double the result: 2(7r)(5t) = 70rt iii) Square the “Last” term: (5t)2 = 25t2 Thus: (7r − 5t)2 = (7r)2 − 2(7r)(5t) + (5t)2 = 49r2 − 70rt + 25t2 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (7r − 5t)2 = 49r2 − 70rt + 25t2 33. Each of the following steps is performed mentally. i) Multiply the terms in the “First” positions: (5b)(3b) = 15b2 ii) Multiply the terms in the “Outer” and “Inner” positions and add the results mentally: −10bc + 18bc = 8bc iii) Multiply the terms in the “Last” positions: (6c)(−2c) = −12c2 Write the answer with no intermediate steps: (5b + 6c)(3b − 2c) = 15b2 + 8bc − 12c2 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (5b + 6c)(3b − 2c) = 15b2 + 8bc − 12c2 35. Note how the terms in the “First” position are identical, as are the terms in the “Last” position, with one set separated by a plus sign and the other with a minus sign. Hence, this is the diﬀerence of squares pattern and we proceed as follows: i) Square the term in the “First” position: (3u)2 = 9u2 ii) Square the term in the “Last” position: (5v)2 = 25v 2 iii) Separate the squares with a minus sign. Second Edition: 2012-2013 5.7. SPECIAL PRODUCTS 325 That is: (3u + 5v)(3u − 5v) = (3u)2 − (5v)2 = 9u2 − 25v 2 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (3u + 5v)(3u − 5v) = 9u2 − 25v 2 37. Note how the terms in the “First” position are identical, as are the terms in the “Last” position, with one set separated by a plus sign and the other with a minus sign. Hence, this is the diﬀerence of squares pattern and we proceed as follows: i) Square the term in the “First” position: (9b3 )2 = 81b6 ii) Square the term in the “Last” position: (10c5 )2 = 100c10 iii) Separate the squares with a minus sign. That is: (9b3 + 10c5 )(9b3 − 10c5 ) = (9b3 )2 − (10c5 )2 = 81b6 − 100c10 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (9b3 + 10c5 )(9b3 − 10c5 ) = 81b6 − 100c10 39. Note how the terms in the “First” position are identical, as are the terms in the “Last” position, with one set separated by a plus sign and the other with a minus sign. Hence, this is the diﬀerence of squares pattern and we proceed as follows: i) Square the term in the “First” position: (9s)2 = 81s2 ii) Square the term in the “Last” position: (4t)2 = 16t2 iii) Separate the squares with a minus sign. That is: (9s − 4t)(9s + 4t) = (9s)2 − (4t)2 = 81s2 − 16t2 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (9s − 4t)(9s + 4t) = 81s2 − 16t2 Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 326 41. Note how the terms in the “First” position are identical, as are the terms in the “Last” position, with one set separated by a plus sign and the other with a minus sign. Hence, this is the diﬀerence of squares pattern and we proceed as follows: i) Square the term in the “First” position: (7x)2 = 49x2 ii) Square the term in the “Last” position: (9y)2 = 81y 2 iii) Separate the squares with a minus sign. That is: (7x − 9y)(7x + 9y) = (7x)2 − (9y)2 = 49x2 − 81y 2 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (7x − 9y)(7x + 9y) = 49x2 − 81y 2 43. Each of the following steps is performed mentally. i) Multiply the terms in the “First” positions: (6a)(2a) = 12a2 ii) Multiply the terms in the “Outer” and “Inner” positions and add the results mentally: 18ab − 12ab = 6ab iii) Multiply the terms in the “Last” positions: (−6b)(3b) = −18b2 Write the answer with no intermediate steps: (6a − 6b)(2a + 3b) = 12a2 + 6ab − 18b2 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (6a − 6b)(2a + 3b) = 12a2 + 6ab − 18b2 45. Note how the terms in the “First” position are identical, as are the terms in the “Last” position, with one set separated by a plus sign and the other with a minus sign. Hence, this is the diﬀerence of squares pattern and we proceed as follows: i) Square the term in the “First” position: (10x)2 = 100x2 ii) Square the term in the “Last” position: (10)2 = 100 Second Edition: 2012-2013 5.7. SPECIAL PRODUCTS 327 iii) Separate the squares with a minus sign. That is: (10x − 10)(10x + 10) = (10x)2 − (10)2 = 100x2 − 100 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (10x − 10)(10x + 10) = 100x2 − 100 47. Each of the following steps is performed mentally. i) Multiply the terms in the “First” positions: (4a)(6a) = 24a2 ii) Multiply the terms in the “Outer” and “Inner” positions and add the results mentally: −12ab + 12ab = 0 iii) Multiply the terms in the “Last” positions: (2b)(−3b) = −6b2 Write the answer with no intermediate steps: (4a + 2b)(6a − 3b) = 24a2 − 6b2 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (4a + 2b)(6a − 3b) = 24a2 − 6b2 49. Each of the following steps is performed mentally. i) Multiply the terms in the “First” positions: (5b)(3b) = 15b2 ii) Multiply the terms in the “Outer” and “Inner” positions and add the results mentally: 10bc − 12bc = −2bc iii) Multiply the terms in the “Last” positions: (−4c)(2c) = −8c2 Write the answer with no intermediate steps: (5b − 4c)(3b + 2c) = 15b2 − 2bc − 8c2 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (5b − 4c)(3b + 2c) = 15b2 − 2bc − 8c2 Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 328 51. Each of the following steps is performed mentally. i) Multiply the terms in the “First” positions: (4b)(6b) = 24b2 ii) Multiply the terms in the “Outer” and “Inner” positions and add the results mentally: −8bc + −36bc = −44bc iii) Multiply the terms in the “Last” positions: (−6c)(−2c) = 12c2 Write the answer with no intermediate steps: (4b − 6c)(6b − 2c) = 24b2 − 44bc + 12c2 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (4b − 6c)(6b − 2c) = 24b2 − 44bc + 12c2 53. Follow these steps: i) Square the ﬁrst term: (11r5 )2 = 121r10 ii) Multiply the “First” and “Last” terms and double the result: 2(11r5 )(9t2 ) = 198r5 t2 iii) Square the “Last” term: (9t2 )2 = 81t4 Thus: (11r5 + 9t2 )2 = (11r5 )2 − 2(11r5 )(9t2 ) + (9t2 )2 = 121r10 + 198r5 t2 + 81t4 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (11r5 + 9t2 )2 = 121r10 + 198r5 t2 + 81t4 55. Each of the following steps is performed mentally. i) Multiply the terms in the “First” positions: (4u)(2u) = 8u2 ii) Multiply the terms in the “Outer” and “Inner” positions and add the results mentally: −24uv + −8uv = −32uv iii) Multiply the terms in the “Last” positions: (−4v)(−6v) = 24v 2 Write the answer with no intermediate steps: (4u − 4v)(2u − 6v) = 8u2 − 32uv + 24v 2 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (4u − 4v)(2u − 6v) = 8u2 − 32uv + 24v 2 Second Edition: 2012-2013 5.7. SPECIAL PRODUCTS 329 57. Follow these steps: i) Square the ﬁrst term: (8r4 )2 = 64r8 ii) Multiply the “First” and “Last” terms and double the result: 2(8r4 )(7t5 ) = 112r4 t5 iii) Square the “Last” term: (7t5 )2 = 49t10 Thus: (8r4 + 7t5 )2 = (8r4 )2 − 2(8r4 )(7t5 ) + (7t5 )2 = 64r8 + 112r4 t5 + 49t10 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (8r4 + 7t5 )2 = 64r8 + 112r4 t5 + 49t10 59. Note how the terms in the “First” position are identical, as are the terms in the “Last” position, with one set separated by a plus sign and the other with a minus sign. Hence, this is the diﬀerence of squares pattern and we proceed as follows: i) Square the term in the “First” position: (4r)2 = 16r2 ii) Square the term in the “Last” position: (3t)2 = 9t2 iii) Separate the squares with a minus sign. That is: (4r + 3t)(4r − 3t) = (4r)2 − (3t)2 = 16r2 − 9t2 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (4r + 3t)(4r − 3t) = 16r2 − 9t2 61. Follow these steps: i) Square the ﬁrst term: (5r)2 = 25r2 ii) Multiply the “First” and “Last” terms and double the result: 2(5r)(6t) = 60rt iii) Square the “Last” term: (6t)2 = 36t2 Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 330 Thus: (5r + 6t)2 = (5r)2 + 2(5r)(6t) + (6t)2 = 25r2 + 60rt + 36t2 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (5r + 6t)2 = 25r2 + 60rt + 36t2 63. Each of the following steps is performed mentally. i) Multiply the terms in the “First” positions: (3x)(2x) = 6x2 ii) Multiply the terms in the “Outer” and “Inner” positions and add the results mentally: 15x − 8x = 7x iii) Multiply the terms in the “Last” positions: (−4)(5) = −20 Write the answer with no intermediate steps: (3x − 4)(2x + 5) = 6x2 + 7x − 20 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (3x − 4)(2x + 5) = 6x2 + 7x − 20 65. Each of the following steps is performed mentally. i) Multiply the terms in the “First” positions: (6b)(2b) = 12b2 ii) Multiply the terms in the “Outer” and “Inner” positions and add the results mentally: 18bc + 8bc = 26bc iii) Multiply the terms in the “Last” positions: (4c)(3c) = 12c2 Write the answer with no intermediate steps: (6b + 4c)(2b + 3c) = 12b2 + 26bc + 12c2 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (6b + 4c)(2b + 3c) = 12b2 + 26bc + 12c2 Second Edition: 2012-2013 5.7. SPECIAL PRODUCTS 331 67. Note how the terms in the “First” position are identical, as are the terms in the “Last” position, with one set separated by a plus sign and the other with a minus sign. Hence, this is the diﬀerence of squares pattern and we proceed as follows: i) Square the term in the “First” position: (11u2 )2 = 121u4 ii) Square the term in the “Last” position: (8w3 )2 = 64w6 iii) Separate the squares with a minus sign. That is: (11u2 + 8w3 )(11u2 − 8w3 ) = (11u2 )2 − (8w3 )2 = 121u4 − 64w6 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (11u2 + 8w3 )(11u2 − 8w3 ) = 121u4 − 64w6 69. Follow these steps: i) Square the ﬁrst term: (4y)2 = 16y 2 ii) Multiply the “First” and “Last” terms and double the result: 2(4y)(3z) = 24yz iii) Square the “Last” term: (3z)2 = 9z 2 Thus: (4y + 3z)2 = (4y)2 + 2(4y)(3z) + (3z)2 = 16y 2 + 24yz + 9z 2 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (4y + 3z)2 = 16y 2 + 24yz + 9z 2 71. Follow these steps: i) Square the ﬁrst term: (7u)2 = 49u2 ii) Multiply the “First” and “Last” terms and double the result: 2(7u)(2v) = 28uv iii) Square the “Last” term: (2v)2 = 4v 2 Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 332 Thus: (7u − 2v)2 = (7u)2 − 2(7u)(2v) + (2v)2 = 49u2 − 28uv + 4v 2 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (7u − 2v)2 = 49u2 − 28uv + 4v 2 73. Each of the following steps is performed mentally. i) Multiply the terms in the “First” positions: (3v)(5v) = 15v 2 ii) Multiply the terms in the “Outer” and “Inner” positions and add the results mentally: 18vw + 10vw = 28vw iii) Multiply the terms in the “Last” positions: (2w)(6w) = 12w2 Write the answer with no intermediate steps: (3v + 2w)(5v + 6w) = 15v 2 + 28vw + 12w2 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (3v + 2w)(5v + 6w) = 15v 2 + 28vw + 12w2 75. Each of the following steps is performed mentally. i) Multiply the terms in the “First” positions: (5x)(6x) = 30x2 ii) Multiply the terms in the “Outer” and “Inner” positions and add the results mentally: 10x − 18x = −8x iii) Multiply the terms in the “Last” positions: (−3)(2) = −6 Write the answer with no intermediate steps: (5x − 3)(6x + 2) = 30x2 − 8x − 6 Note: You should practice this pattern until you can go straight from the problem statement to the answer without writing down any intermediate work, as in: (5x − 3)(6x + 2) = 30x2 − 8x − 6 Second Edition: 2012-2013 5.7. SPECIAL PRODUCTS 333 77. The two shaded squares in have areas A1 = x2 and A3 = 100, respectively. The two unshaded rectangles have areas A2 = 10x and A4 = 10x. x 10 10 A2 = 10x A3 = 100 10 x A1 = x 2 A4 = 10x x x 10 Summing these four areas gives us the area of the entire ﬁgure. A = A1 + A2 + A3 + A4 = x2 + 10x + 100 + 10x = x2 + 20x + 100 However, a faster solution is found by squaring the side of the square using the shortcut (a + b)2 = a2 + 2ab + b2 . A = (x + 10)2 = x2 + 20x + 100 79. After cutting four squares with side x inches from each corner of the original piece of cardboard (measuring 12 inches on each side), the dashed edges that will become the eventual edges of the base of the cardboard box now measure 12 − 2x inches. The sides are then folded upwards to form a cardboard box with no top. x x x x 2x 12 − 2x x x 12 − 2x 12 − 2x 12 x 12 − 2x 12 − x x 12 − 2x 12 Second Edition: 2012-2013 CHAPTER 5. POLYNOMIALS 334 The volume of the box is found by taking the product of the length, width, and height of the box. V = LW H V = (12 − 2x)(12 − 2x)x Changing the order of multiplication and using exponents, this can be written more concisely. V = x(12 − 2x)2 We can use (a − b)2 = a2 − 2ab + b2 to square the binomial. V = x(144 − 48x + 4x2 ) Finally, we can distribute the x. V = 144x − 48x2 + 4x3 Using function notation, we can also write V (x) = 144x − 48x2 + 4x3 . To ﬁnd the volume when the edge of the square cut from each corner measures 1.25 inches, substitute 1.25 for x in the polynomial. V (2) = 144(1.25) − 48(1.25)2 + 4(1.25)3 Use your calculator to obtain the following result. V (2) = 112.8125 Thus, the volume of the box is approximately 113 cubic inches. Second Edition: 2012-2013 Chapter 6 Factoring 6.1 The Greatest Common Factor 1. First, list all possible ways that we can express 42 as a product of two positive integers: 42 = 1 · 42 42 = 6 · 7 42 = 2 · 21 42 = 3 · 14 Therefore, the list of divisors of 42 is: {1, 2, 3, 6, 7, 14, 21, 42} 3. First, list all possible ways that we can express 44 as a product of two positive integers: 44 = 1 · 44 44 = 2 · 22 44 = 4 · 11 Therefore, the list of divisors of 44 is: {1, 2, 4, 11, 22, 44} 5. First, list all possible ways that we can express 51 as a product of two positive integers: 51 = 1 · 51 51 = 3 · 17 Therefore, the list of divisors of 51 is: {1, 3, 17, 51} 335 CHAPTER 6. FACTORING 336 7. First, list the positive divisors of 36: 1, 2, 3, 4, 6, 9, 12, 18, 36 Secondly, list the positive divisors of 42: 1, 2, 3, 6, 7, 14, 21, 42 Finally, list the positive divisors that are in common. 1, 2, 3, 6 9. First, list the positive divisors of 78: 1, 2, 3, 6, 13, 26, 39, 78 Secondly, list the positive divisors of 54: 1, 2, 3, 6, 9, 18, 27, 54 Finally, list the positive divisors that are in common. 1, 2, 3, 6 11. First, list the positive divisors of 8: 1, 2, 4, 8 Secondly, list the positive divisors of 76: 1, 2, 4, 19, 38, 76 Finally, list the positive divisors that are in common. 1, 2, 4 13. We’re asked to ﬁnd the greatest common divisor of 76 and 8. Therefore, we must try to ﬁnd the largest number that divides evenly (zero remainder) into both 76 and 8. For some folks, the number 4 just pops into their heads. However, if the number doesn’t just “pop into your head,” then you can: i) List the positive divisors of 76: 1, 2, 4, 19, 38, 76 ii) List the positive divisors of 8: 1, 2, 4, 8 iii) List the positive divisors that are in common. 1, 2, 4 The greatest common divisor is therefore 4. Second Edition: 2012-2013 6.1. THE GREATEST COMMON FACTOR 337 15. We’re asked to ﬁnd the greatest common divisor of 32 and 36. Therefore, we must try to ﬁnd the largest number that divides evenly (zero remainder) into both 32 and 36. For some folks, the number 4 just pops into their heads. However, if the number doesn’t just “pop into your head,” then you can: i) List the positive divisors of 32: 1, 2, 4, 8, 16, 32 ii) List the positive divisors of 36: 1, 2, 3, 4, 6, 9, 12, 18, 36 iii) List the positive divisors that are in common. 1, 2, 4 The greatest common divisor is therefore 4. 17. We’re asked to ﬁnd the greatest common divisor of 24 and 28. Therefore, we must try to ﬁnd the largest number that divides evenly (zero remainder) into both 24 and 28. For some folks, the number 4 just pops into their heads. However, if the number doesn’t just “pop into your head,” then you can: i) List the positive divisors of 24: 1, 2, 3, 4, 6, 8, 12, 24 ii) List the positive divisors of 28: 1, 2, 4, 7, 14, 28 iii) List the positive divisors that are in common. 1, 2, 4 The greatest common divisor is therefore 4. 19. Prime factor each number and place the result in compact form using exponents. 600 = 23 · 31 · 52 1080 = 23 · 33 · 51 Second Edition: 2012-2013 CHAPTER 6. FACTORING 338 Write each prime factor that appears above to the highest power that appears in common. GCD = 23 · 31 · 51 Raise each factor to highest power that appears in common. Expand and simplify. Expand: 23 = 8, 31 = 3, and 51 = 5 Multiply. =8·3·5 = 120 Therefore, GCD(600, 1080) = 120. 21. Prime factor each number and place the result in compact form using exponents. 1800 = 23 · 32 · 52 2250 = 21 · 32 · 53 Write each prime factor that appears above to the highest power that appears in common. GCD = 21 · 32 · 52 Raise each factor to highest power that appears in common. Expand and simplify. Expand: 21 = 2, 32 = 9, and 52 = 25 Multiply. = 2 · 9 · 25 = 450 Therefore, GCD(1800, 2250) = 450. 23. Prime factor each number and place the result in compact form using exponents. 600 = 23 · 31 · 52 450 = 21 · 32 · 52 Write each prime factor that appears above to the highest power that appears in common. GCD = 21 · 31 · 52 Second Edition: 2012-2013 Raise each factor to highest power that appears in common. 6.1. THE GREATEST COMMON FACTOR 339 Expand and simplify. = 2 · 3 · 25 Expand: 21 = 2, 31 = 3, and 52 = 25 = 150 Multiply. Therefore, GCD(600, 450) = 150. 25. To ﬁnd the GCF of 16b4 and 56b9 , we note that: 1. The greatest common factor (divisor) of 16 and 56 is 8. 2. The monomials 16b4 and 56b9 have the variable b in common. 3. The highest power of b in common is b4 . Thus, the greatest common factor is GCF(16b4 , 56b9 ) = 8b4 . Note what happens when we write each of the given monomials as a product of the greatest common factor and a second monomial: 16b4 = 8b4 · 2 56b9 = 8b4 · 7b5 Note how the set of second monomial factors (2 and 7b5 ) contain no additional common factors. 27. To ﬁnd the GCF of 35z 2 and 49z 7 , we note that: 1. The greatest common factor (divisor) of 35 and 49 is 7. 2. The monomials 35z 2 and 49z 7 have the variable z in common. 3. The highest power of z in common is z 2 . Thus, the greatest common factor is GCF(35z 2 , 49z 7) = 7z 2 . Note what happens when we write each of the given monomials as a product of the greatest common factor and a second monomial: 35z 2 = 7z 2 · 5 49z 7 = 7z 2 · 7z 5 Note how the set of second monomial factors (5 and 7z 5 ) contain no additional common factors. Second Edition: 2012-2013 CHAPTER 6. FACTORING 340 29. To ﬁnd the GCF of 56x3 y 4 and 16x2 y 5 , we note that: 1. The greatest common factor (divisor) of 56 and 16 is 8. 2. The monomials 56x3 y 4 and 16x2 y 5 have the variables x and y in common. 3. The highest power of x in common is x2 . The highest power of y in common is y 4 . Thus, the greatest common factor is GCF(56x3 y 4 , 16x2 y 5 ) = 8x2 y 4 . Note what happens when we write each of the given monomials as a product of the greatest common factor and a second monomial: 56x3 y 4 = 8x2 y 4 · 7x 16x2 y 5 = 8x2 y 4 · 2y Note how the set of second monomial factors (7x and 2y) contain no additional common factors. 31. To ﬁnd the GCF of 24s4 t5 and 16s3 t6 , we note that: 1. The greatest common factor (divisor) of 24 and 16 is 8. 2. The monomials 24s4 t5 and 16s3 t6 have the variables s and t in common. 3. The highest power of s in common is s3 . The highest power of t in common is t5 . Thus, the greatest common factor is GCF(24s4 t5 , 16s3 t6 ) = 8s3 t5 . Note what happens when we write each of the given monomials as a product of the greatest common factor and a second monomial: 24s4 t5 = 8s3 t5 · 3s 16s3 t6 = 8s3 t5 · 2t Note how the set of second monomial factors (3s and 2t) contain no additional common factors. 33. To ﬁnd the GCF of 18y 7 , 45y 6 , and 27y 5 , we note that: 1. The greatest common factor (divisor) of 18, 45, and 27 is 9. 2. The monomials 18y 7 , 45y 6 , and 27y 5 have the variable y in common. 3. The highest power of y in common is y 5 . Second Edition: 2012-2013 6.1. THE GREATEST COMMON FACTOR 341 Thus, the greatest common factor is GCF(18y 7 , 45y 6, 27y 5 ) = 9y 5 . Note what happens when we write each of the given monomials as a product of the greatest common factor and a second monomial: 18y 7 = 9y 5 · 2y 2 45y 6 = 9y 5 · 5y 27y 5 = 9y 5 · 3 Note how the set of second monomial factors (2y 2 , 5y, and 3) contain no additional common factors. 35. To ﬁnd the GCF of 9a6 , 6a5 , and 15a4 , we note that: 1. The greatest common factor (divisor) of 9, 6, and 15 is 3. 2. The monomials 9a6 , 6a5 , and 15a4 have the variable a in common. 3. The highest power of a in common is a4 . Thus, the greatest common factor is GCF(9a6 , 6a5 , 15a4 ) = 3a4 . Note what happens when we write each of the given monomials as a product of the greatest common factor and a second monomial: 9a6 = 3a4 · 3a2 6a5 = 3a4 · 2a 15a4 = 3a4 · 5 Note how the set of second monomial factors (3a2 , 2a, and 5) contain no additional common factors. 37. The greatest common factor (GCF) of 25a2 , 10a and 20 is 5. Factor out the GCF. 25a2 + 10a + 20 = 5 · 5a2 + 5 · 2a + 5 · 4 = 5(5a2 + 2a + 4) Check: Multiply. Distribute the 5. 5(5a2 + 2a + 4) = 5 · 5a2 + 5 · 2a + 5 · 4 = 25a2 + 10a + 20 That’s the original polynomial, so we factored correctly. Second Edition: 2012-2013 CHAPTER 6. FACTORING 342 39. The greatest common factor (GCF) of 35s2 , 25s and 45 is 5. Factor out the GCF. 35s2 + 25s + 45 = 5 · 7s2 + 5 · 5s + 5 · 9 = 5(7s2 + 5s + 9) Check: Multiply. Distribute the 5. 5(7s2 + 5s + 9) = 5 · 7s2 + 5 · 5s + 5 · 9 = 35s2 + 25s + 45 That’s the original polynomial, so we factored correctly. 41. The greatest common factor (GCF) of 16c3 , 32c2 and 36c is 4c. Factor out the GCF. 16c3 + 32c2 + 36c = 4c · 4c2 + 4c · 8c + 4c · 9 = 4c(4c2 + 8c + 9) Check: Multiply. Distribute the 4c. 4c(4c2 + 8c + 9) = 4c · 4c2 + 4c · 8c + 4c · 9 = 16c3 + 32c2 + 36c That’s the original polynomial, so we factored correctly. 43. The greatest common factor (GCF) of 42s3 , 24s2 and 18s is 6s. Factor out the GCF. 42s3 + 24s2 + 18s = 6s · 7s2 + 6s · 4s + 6s · 3 = 6s(7s2 + 4s + 3) Check: Multiply. Distribute the 6s. 6s(7s2 + 4s + 3) = 6s · 7s2 + 6s · 4s + 6s · 3 = 42s3 + 24s2 + 18s That’s the original polynomial, so we factored correctly. 45. The greatest common factor (GCF) of 35s7 , 49s6 and 63s5 is 7s5 . Factor out the GCF. 35s7 + 49s6 + 63s5 = 7s5 · 5s2 + 7s5 · 7s + 7s5 · 9 = 7s5 (5s2 + 7s + 9) Check: Multiply. Distribute the 7s5 . 7s5 (5s2 + 7s + 9) = 7s5 · 5s2 + 7s5 · 7s + 7s5 · 9 = 35s7 + 49s6 + 63s5 That’s the original polynomial, so we factored correctly. Second Edition: 2012-2013 6.1. THE GREATEST COMMON FACTOR 343 47. The greatest common factor (GCF) of 14b7 , 35b6 and 56b5 is 7b5 . Factor out the GCF. 14b7 + 35b6 + 56b5 = 7b5 · 2b2 + 7b5 · 5b + 7b5 · 8 = 7b5 (2b2 + 5b + 8) Check: Multiply. Distribute the 7b5 . 7b5 (2b2 + 5b + 8) = 7b5 · 2b2 + 7b5 · 5b + 7b5 · 8 = 14b7 + 35b6 + 56b5 That’s the original polynomial, so we factored correctly. 49. The greatest common factor (GCF) of 54y 5 z 3 , 30y 4 z 4 and 36y 3z 5 is 6y 3 z 3 . Factor out the GCF. 54y 5 z 3 + 30y 4 z 4 + 36y 3 z 5 = 6y 3 z 3 · 9y 2 + 6y 3 z 3 · 5yz + 6y 3 z 3 · 6z 2 = 6y 3 z 3 (9y 2 + 5yz + 6z 2 ) Check: Multiply. Distribute the 6y 3 z 3 . 6y 3 z 3 (9y 2 + 5yz + 6z 2 ) = 6y 3 z 3 · 9y 2 + 6y 3 z 3 · 5yz + 6y 3 z 3 · 6z 2 = 54y 5 z 3 + 30y 4 z 4 + 36y 3 z 5 That’s the original polynomial, so we factored correctly. 51. The greatest common factor (GCF) of 45s4 t3 , 40s3 t4 and 15s2 t5 is 5s2 t3 . Factor out the GCF. 45s4 t3 + 40s3 t4 + 15s2 t5 = 5s2 t3 · 9s2 + 5s2 t3 · 8st + 5s2 t3 · 3t2 = 5s2 t3 (9s2 + 8st + 3t2 ) Check: Multiply. Distribute the 5s2 t3 . 5s2 t3 (9s2 + 8st + 3t2 ) = 5s2 t3 · 9s2 + 5s2 t3 · 8st + 5s2 t3 · 3t2 = 45s4 t3 + 40s3 t4 + 15s2 t5 That’s the original polynomial, so we factored correctly. Second Edition: 2012-2013 CHAPTER 6. FACTORING 344 53. In this case, the greatest common factor (GCF) is 2w − 3. 7w(2w − 3) − 8(2w − 3) = 7w · (2w − 3) − 8 · (2w − 3) = (7w − 8)(2w − 3) Because of the commutative property of multiplication, it is equally valid to pull the GCF out in front. 7w(2w − 3) − 8(2w − 3) = (2w − 3) · 7w − (2w − 3) · 8 = (2w − 3)(7w − 8) Note that the order of factors diﬀers from the ﬁrst solution, but because of the commutative property of multiplication, the order does not matter. The answers are the same. 55. In this case, the greatest common factor (GCF) is 5r − 1. 9r(5r − 1) + 8(5r − 1) = 9r · (5r − 1) + 8 · (5r − 1) = (9r + 8)(5r − 1) Because of the commutative property of multiplication, it is equally valid to pull the GCF out in front. 9r(5r − 1) + 8(5r − 1) = (5r − 1) · 9r + (5r − 1) · 8 = (5r − 1)(9r + 8) Note that the order of factors diﬀers from the ﬁrst solution, but because of the commutative property of multiplication, the order does not matter. The answers are the same. 57. In this case, the greatest common factor (GCF) is 6(2a + 5). 48a(2a + 5) − 42(2a + 5) = 6(2a + 5) · 8a − 6(2a + 5) · 7 = 6(2a + 5)(8a − 7) Alternate solution: It is possible that you might fail to notice that 15 and 12 are divisible by 3, factoring out only a common factor 2a + 5. 48a(2a + 5) − 42(2a + 5) = 48a · (2a + 5) − 42 · (2a + 5) = (48a − 42)(2a + 5) However, you now need to notice that you can continue, factoring out a 6 from both 48a and −42. = 6(8a − 7)(2a + 5) Note that the order of factors diﬀers from the ﬁrst solution, but because of the commutative property of multiplication, the order does not matter. The answers are the same. Second Edition: 2012-2013 6.1. THE GREATEST COMMON FACTOR 345 59. In this case, the greatest common factor (GCF) is 7(2a − 1). 56a(2a − 1) − 21(2a − 1) = 7(2a − 1) · 8a − 7(2a − 1) · 3 = 7(2a − 1)(8a − 3) Alternate solution: It is possible that you might fail to notice that 15 and 12 are divisible by 3, factoring out only a common factor 2a − 1. 56a(2a − 1) − 21(2a − 1) = 56a · (2a − 1) − 21 · (2a − 1) = (56a − 21)(2a − 1) However, you now need to notice that you can continue, factoring out a 7 from both 56a and −21. = 7(8a − 3)(2a − 1) Note that the order of factors diﬀers from the ﬁrst solution, but because of the commutative property of multiplication, the order does not matter. The answers are the same. 61. We “group” the ﬁrst and second terms, noting that we can factor x out of both of these terms. Then we “group” the third and fourth terms, noting that we can factor −9 out of both of these terms. x2 + 2x − 9x − 18 = x (x + 2) − 9 (x + 2) Note that we can now factor x + 2 out of both of these terms. = (x − 9)(x + 2) 63. We “group” the ﬁrst and second terms, noting that we can factor x out of both of these terms. Then we “group” the third and fourth terms, noting that we can factor 6 out of both of these terms. x2 + 3x + 6x + 18 = x (x + 3) + 6 (x + 3) Note that we can now factor x + 3 out of both of these terms. = (x + 6)(x + 3) Second Edition: 2012-2013 CHAPTER 6. FACTORING 346 65. We “group” the ﬁrst and second terms, noting that we can factor x out of both of these terms. Then we “group” the third and fourth terms, noting that we can factor −3 out of both of these terms. x2 + 6x + 3x + 18 = x (x − 6) − 3 (x − 6) Note that we can now factor x − 6 out of both of these terms. = (x − 3)(x − 6) 67. We “group” the ﬁrst and second terms, noting that we can factor x out of both of these terms. Then we “group” the third and fourth terms, noting that we can factor 3 out of both of these terms. x2 − 9x + 3x − 27 = x (x − 9) + 3 (x − 9) Note that we can now factor x − 9 out of both of these terms. = (x + 3)(x − 9) 69. We “group” the ﬁrst and second terms, noting that we can factor x out of both of these terms. Then we “group” the third and fourth terms, noting that we can factor −7 out of both of these terms. 8x2 + 3x − 56x − 21 = x (8x + 3) − 7 (8x + 3) Note that we can now factor 8x + 3 out of both of these terms. = (x − 7)(8x + 3) 71. We “group” the ﬁrst and second terms, noting that we can factor 9x out of both of these terms. Then we “group” the third and fourth terms, noting that we can factor −5 out of both of these terms. 9x2 + 36x − 5x − 20 = 9x (x + 4) − 5 (x + 4) Note that we can now factor x + 4 out of both of these terms. = (9x − 5)(x + 4) Second Edition: 2012-2013 6.2. SOLVING NONLINEAR EQUATIONS 347 73. We “group” the ﬁrst and second terms, noting that we can factor x out of both of these terms. Then we “group” the third and fourth terms, noting that we can factor −8 out of both of these terms. 6x2 − 7x − 48x + 56 = x (6x − 7) − 8 (6x − 7) Note that we can now factor 6x − 7 out of both of these terms. = (x − 8)(6x − 7) 75. We “group” the ﬁrst and second terms, noting that we can factor 2x out of both of these terms. Then we “group” the third and fourth terms, noting that we can factor 7 out of both of these terms. 2x2 + 12x + 7x + 42 = 2x (x + 6) + 7 (x + 6) Note that we can now factor x + 6 out of both of these terms. = (2x + 7)(x + 6) 6.2 Solving Nonlinear Equations 1. The product of two factors equals zero. (9x + 2)(8x + 3) = 0 Hence, at least one of the factors must equal zero, so set each factor equal to zero and solve the resulting equations for x. 9x + 2 = 0 9x = −2 2 x=− 9 or 8x + 3 = 0 8x = −3 3 x=− 8 Hence, the solutions are x = −2/9 and x = −3/8 Second Edition: 2012-2013 CHAPTER 6. FACTORING 348 3. The product of three factors equals zero. x(4x + 7)(9x − 8) = 0 Hence, at least one of the factors must equal zero, so set each factor equal to zero and solve the resulting equations for x. x=0 or 4x + 7 = 0 4x = −7 7 x=− 4 or 9x − 8 = 0 9x = 8 8 x= 9 Hence, the solutions are x = 0, x = −7/4, and x = 8/9 5. The product of two factors equals zero. −9x(9x + 4) = 0 Hence, at least one of the factors must equal zero, so set each factor equal to zero and solve the resulting equations for x. −9x = 0 or x=0 or 9x + 4 = 0 9x = −4 4 x=− 9 Hence, the solutions are x = 0 and x = −4/9 7. The product of two factors equals zero. (x + 1)(x + 6) = 0 Hence, at least one of the factors must equal zero, so set each factor equal to zero and solve the resulting equations for x. x+1=0 or x = −1 x+6=0 x = −6 Hence, the solutions are x = −1 and x = −6 9. The equation x2 + 7x = 9x + 63 contains a power of x higher than one (it contains an x2 ). Hence, this equation is nonlinear. Second Edition: 2012-2013 6.2. SOLVING NONLINEAR EQUATIONS 349 11. The highest power of x present in the equation 6x − 2 = 5x − 8 is one. Hence, this equation is linear. 13. The equation 7x2 = −2x contains a power of x higher than one (it contains an x2 ). Hence, this equation is nonlinear. 15. The equation 3x2 + 8x = −9 contains a power of x higher than one (it contains an x2 ). Hence, this equation is nonlinear. 17. The highest power of x present in the equation −3x + 6 = −9 is one. Hence, this equation is linear. 19. The equation 3x + 8 = 9 contains no power of x higher than one. Hence, this equation is linear. Move all terms containing x to one side of the equation and all terms not containing x to the other side of the equation. 3x + 8 = 9 3x = 9 − 8 Original equation is linear. Subtract 8 from both sides. Note that all terms containing x are now on one side of the equation, while all terms that do not contain x are on the other side of the equation. 3x = 1 1 x= 3 Simplify Divide both sides by 3. 21. Because the instruction is “solve for x,” and the highest power of x is larger than one, the equation 9x2 = −x is nonlinear. Hence, the strategy requires that we move all terms to one side of the equation, making one side zero. 9x2 = −x 2 9x + x = 0 Original equation. Add x to both sides. Note how we have succeeded in moving all terms to one side of the equation, making one side equal to zero. To ﬁnish the solution, we factor out the GCF on the left-hand side. x(9x + 1) = 0 Factor out the GCF. Second Edition: 2012-2013 CHAPTER 6. FACTORING 350 Note that we now have a product of two factors that equals zero. By the zero product property, either the ﬁrst factor is zero or the second factor is zero. x=0 or 9x + 1 = 0 9x = −1 1 x=− 9 Hence, the solutions are x = 0 and x = −1/9. 23. The equation 3x + 9 = 8x + 7 contains no power of x higher than one. Hence, this equation is linear. Move all terms containing x to one side of the equation and all terms not containing x to the other side of the equation. 3x + 9 = 8x + 7 3x + 9 − 8x = 7 Original equation is linear. Subtract 8x from both sides. 3x − 8x = 7 − 9 Subtract 9 from both sides. Note that all terms containing x are now on one side of the equation, while all terms that do not contain x are on the other side of the equation. −5x = −2 2 x= 5 Simplify Divide both sides by −5. 25. Because the instruction is “solve for x,” and the highest power of x is larger than one, the equation 8x2 = −2x is nonlinear. Hence, the strategy requires that we move all terms to one side of the equation, making one side zero. 8x2 = −2x Original equation. 2 8x + 2x = 0 Add 2x to both sides. Note how we have succeeded in moving all terms to one side of the equation, making one side equal to zero. To ﬁnish the solution, we factor out the GCF on the left-hand side. 2x(4x + 1) = 0 Factor out the GCF. Note that we now have a product of two factors that equals zero. By the zero product property, either the ﬁrst factor is zero or the second factor is zero. 2x = 0 x=0 4x + 1 = 0 4x = −1 1 x=− 4 Hence, the solutions are x = 0 and x = −1/4. Second Edition: 2012-2013 or 6.2. SOLVING NONLINEAR EQUATIONS 351 27. The equation 9x + 2 = 7 contains no power of x higher than one. Hence, this equation is linear. Move all terms containing x to one side of the equation and all terms not containing x to the other side of the equation. 9x + 2 = 7 9x = 7 − 2 Original equation is linear. Subtract 2 from both sides. Note that all terms containing x are now on one side of the equation, while all terms that do not contain x are on the other side of the equation. 9x = 5 5 x= 9 Simplify Divide both sides by 9. 29. Because the instruction is “solve for x,” and the highest power of x is larger than one, the equation 9x2 = 6x is nonlinear. Hence, the strategy requires that we move all terms to one side of the equation, making one side zero. 9x2 = 6x Original equation. 2 9x − 6x = 0 Subtract 6x from both sides. Note how we have succeeded in moving all terms to one side of the equation, making one side equal to zero. To ﬁnish the solution, we factor out the GCF on the left-hand side. 3x(3x − 2) = 0 Factor out the GCF. Note that we now have a product of two factors that equals zero. By the zero product property, either the ﬁrst factor is zero or the second factor is zero. 3x = 0 x=0 or 3x − 2 = 0 3x = 2 2 x= 3 Hence, the solutions are x = 0 and x = 2/3. 31. Because the instruction is “solve for x,” and the highest power of x is larger than one, the equation 7x2 = −4x is nonlinear. Hence, the strategy requires that we move all terms to one side of the equation, making one side zero. 7x2 = −4x 2 7x + 4x = 0 Original equation. Add 4x to both sides. Second Edition: 2012-2013 CHAPTER 6. FACTORING 352 Note how we have succeeded in moving all terms to one side of the equation, making one side equal to zero. To ﬁnish the solution, we factor out the GCF on the left-hand side. x(7x + 4) = 0 Factor out the GCF. Note that we now have a product of two factors that equals zero. By the zero product property, either the ﬁrst factor is zero or the second factor is zero. x=0 or 7x + 4 = 0 7x = −4 4 x=− 7 Hence, the solutions are x = 0 and x = −4/7. 33. The equation 7x + 2 = 4x + 7 contains no power of x higher than one. Hence, this equation is linear. Move all terms containing x to one side of the equation and all terms not containing x to the other side of the equation. 7x + 2 = 4x + 7 7x + 2 − 4x = 7 7x − 4x = 7 − 2 Original equation is linear. Subtract 4x from both sides. Subtract 2 from both sides. Note that all terms containing x are now on one side of the equation, while all terms that do not contain x are on the other side of the equation. 3x = 5 5 x= 3 Simplify Divide both sides by 3. 35. The equation 63x2 + 56x + 54x + 48 = 0 contains a power of x higher than one. Hence, this equation is nonlinear so we must start by moving all terms to one side of the equation, making one side equal to zero. However, this is already done, so let’s proceed by factoring by grouping. We can factor 7x out of the ﬁrst two terms and 6 out of the second two terms. 63x2 + 56x + 54x + 48 = 0 7x (9x + 8) + 6 (9x + 8) = 0 Note that we can now factor 9x + 8 out of both of these terms. (7x + 6)(9x + 8) = 0 Second Edition: 2012-2013 6.2. SOLVING NONLINEAR EQUATIONS 353 Use the zero product property to set each factor equal to zero. Solve the resulting equations for x. 7x + 6 = 0 or 9x + 8 = 0 7x = −6 6 x=− 7 9x = −8 8 x=− 9 Hence, the solutions are x = −6/7 and x = −8/9. 37. The equation 16x2 − 18x + 40x − 45 = 0 contains a power of x higher than one. Hence, this equation is nonlinear so we must start by moving all terms to one side of the equation, making one side equal to zero. However, this is already done, so let’s proceed by factoring by grouping. We can factor 2x out of the ﬁrst two terms and 5 out of the second two terms. 16x2 − 18x + 40x − 45 = 0 2x (8x − 9) + 5 (8x − 9) = 0 Note that we can now factor 8x − 9 out of both of these terms. (2x + 5)(8x − 9) = 0 Use the zero product property to set each factor equal to zero. Solve the resulting equations for x. 2x + 5 = 0 2x = −5 5 x=− 2 or 8x − 9 = 0 8x = 9 9 x= 8 Hence, the solutions are x = −5/2 and x = 9/8. 39. The equation 45x2 + 18x + 20x + 8 = 0 contains a power of x higher than one. Hence, this equation is nonlinear so we must start by moving all terms to one side of the equation, making one side equal to zero. However, this is already done, so let’s proceed by factoring by grouping. We can factor 9x out of the ﬁrst two terms and 4 out of the second two terms. 45x2 + 18x + 20x + 8 = 0 9x (5x + 2) + 4 (5x + 2) = 0 Second Edition: 2012-2013 CHAPTER 6. FACTORING 354 Note that we can now factor 5x + 2 out of both of these terms. (9x + 4)(5x + 2) = 0 Use the zero product property to set each factor equal to zero. Solve the resulting equations for x. 9x + 4 = 0 or 5x + 2 = 0 9x = −4 4 x=− 9 5x = −2 2 x=− 5 Hence, the solutions are x = −4/9 and x = −2/5. 41. The equation x2 + 10x + 4x + 40 = 0 contains a power of x higher than one. Hence, this equation is nonlinear so we must start by moving all terms to one side of the equation, making one side equal to zero. However, this is already done, so let’s proceed by factoring by grouping. We can factor x out of the ﬁrst two terms and 4 out of the second two terms. x2 + 10x + 4x + 40 = 0 x (x + 10) + 4 (x + 10) = 0 Note that we can now factor x + 10 out of both of these terms. (x + 4)(x + 10) = 0 Use the zero product property to set each factor equal to zero. Solve the resulting equations for x. x+4=0 or x + 10 = 0 x = −4 x = −10 Hence, the solutions are x = −4 and x = −10. 43. The equation x2 + 6x − 11x − 66 = 0 contains a power of x higher than one. Hence, this equation is nonlinear so we must start by moving all terms to one side of the equation, making one side equal to zero. However, this is already done, so let’s proceed by factoring by grouping. We can factor x out of the ﬁrst two terms and −11 out of the second two terms. Second Edition: 2012-2013 6.2. SOLVING NONLINEAR EQUATIONS 355 x2 + 6x − 11x − 66 = 0 x (x + 6) − 11 (x + 6) = 0 Note that we can now factor x + 6 out of both of these terms. (x − 11)(x + 6) = 0 Use the zero product property to set each factor equal to zero. Solve the resulting equations for x. x − 11 = 0 x = 11 or x+6=0 x = −6 Hence, the solutions are x = 11 and x = −6. 45. The equation 15x2 − 24x + 35x − 56 = 0 contains a power of x higher than one. Hence, this equation is nonlinear so we must start by moving all terms to one side of the equation, making one side equal to zero. However, this is already done, so let’s proceed by factoring by grouping. We can factor 3x out of the ﬁrst two terms and 7 out of the second two terms. 15x2 − 24x + 35x − 56 = 0 3x (5x − 8) + 7 (5x − 8) = 0 Note that we can now factor 5x − 8 out of both of these terms. (3x + 7)(5x − 8) = 0 Use the zero product property to set each factor equal to zero. Solve the resulting equations for x. 3x + 7 = 0 3x = −7 7 x=− 3 or 5x − 8 = 0 5x = 8 8 x= 5 Hence, the solutions are x = −7/3 and x = 8/5. Second Edition: 2012-2013 CHAPTER 6. FACTORING 356 47. The equation x2 + 2x + 9x + 18 = 0 contains a power of x higher than one. Hence, this equation is nonlinear so we must start by moving all terms to one side of the equation, making one side equal to zero. However, this is already done, so let’s proceed by factoring by grouping. We can factor x out of the ﬁrst two terms and 9 out of the second two terms. x2 + 2x + 9x + 18 = 0 x (x + 2) + 9 (x + 2) = 0 Note that we can now factor x + 2 out of both of these terms. (x + 9)(x + 2) = 0 Use the zero product property to set each factor equal to zero. Solve the resulting equations for x. x+9=0 or x+2=0 x = −9 x = −2 Hence, the solutions are x = −9 and x = −2. 49. The equation x2 + 4x − 8x − 32 = 0 contains a power of x higher than one. Hence, this equation is nonlinear so we must start by moving all terms to one side of the equation, making one side equal to zero. However, this is already done, so let’s proceed by factoring by grouping. We can factor x out of the ﬁrst two terms and −8 out of the second two terms. x2 + 4x − 8x − 32 = 0 x (x + 4) − 8 (x + 4) = 0 Note that we can now factor x + 4 out of both of these terms. (x − 8)(x + 4) = 0 Use the zero product property to set each factor equal to zero. Solve the resulting equations for x. x−8=0 or x=8 Hence, the solutions are x = 8 and x = −4. Second Edition: 2012-2013 x+4=0 x = −4 6.2. SOLVING NONLINEAR EQUATIONS 357 51. Algebraic solution. The equation is nonlinear, so make one side zero by moving all terms containing x to one side of the equation. x2 = −4x The equation is nonlinear, so make one side zero. x2 + 4x = 0 Add 4x to both sides. x(x + 4) = 0 Factor out GCF. Use the zero product property to set both factors equal to zero, then solve the resulting equations. x=0 or x+4=0 x = −4 Hence, the solutions are x = 0 and x = −4. Calculator solution. Load each side of the equation x2 = −4x into Y1 and Y2 in the Y= menu, then select 6:ZStandard from the ZOOM menu to produce the following graph. We need both points of intersection to be visible in the viewing window. Adjust the WINDOW parameters as shown, then push the GRAPH button to produce the accompanying graph. Next, use the 5:intersect utility from the CALC menu to ﬁnd the points of intersection. Second Edition: 2012-2013 CHAPTER 6. FACTORING 358 Report the results on your homework as follows. y y = x2 30 −10 −4 10 0 −10 x y = −4x Hence, the solutions of x2 = −4x are x = −4 and x = 0. Note how these agree with the algebraic solution. 53. Algebraic solution. The equation is nonlinear, so make one side zero by moving all terms containing x to one side of the equation. x2 = 5x The equation is nonlinear, so make one side zero. x2 − 5x = 0 x(x − 5) = 0 Subtract 5x from both sides. Factor out GCF. Use the zero product property to set both factors equal to zero, then solve the resulting equations. x=0 or x−5= 0 x=5 Hence, the solutions are x = 0 and x = 5. Calculator solution. Load each side of the equation x2 = 5x into Y1 and Y2 in the Y= menu, then select 6:ZStandard from the ZOOM menu to produce the following graph. Second Edition: 2012-2013 6.2. SOLVING NONLINEAR EQUATIONS 359 We need both points of intersection to be visible in the viewing window. Adjust the WINDOW parameters as shown, then push the GRAPH button to produce the accompanying graph. Next, use the 5:intersect utility from the CALC menu to ﬁnd the points of intersection. Report the results on your homework as follows. y 2 y=x y = 5x 50 −10 0 5 10 x −10 Hence, the solutions of x2 = 5x are x = 0 and x = 5. Note how these agree with the algebraic solution. Second Edition: 2012-2013 CHAPTER 6. FACTORING 360 55. Algebraic solution. The equation is nonlinear, so make one side zero. This is already done, so factor out the GCF. x2 + 7x = 0 x(x + 7) = 0 Original equation is nonlinear. Factor out GCF. Use the zero product property to set both factors equal to zero, then solve the resulting equations. x=0 or x+7=0 x = −7 Hence, the solutions are x = 0 and x = −7. Calculator solution. Load the left-hand side of the equation x2 + 7x = 0 into Y1 in the Y= menu, then select 6:ZStandard from the ZOOM menu to produce the following graph. Both x-intercepts are visible, but we really should adjust the viewing window so that the vertex of the parabola is visible in the viewing window as well. Adjust the WINDOW parameters as shown, then push the GRAPH button to produce the accompanying graph. Next, use the 2:zero utility from the CALC menu to ﬁnd the points of intersection. Second Edition: 2012-2013 6.2. SOLVING NONLINEAR EQUATIONS 361 Report the results on your homework as follows. y y = x2 + 7x 20 −15 −7 5 0 x −20 Hence, the solutions of x2 + 7x = 0 are x = −7 and x = 0. Note how these agree with the algebraic solution. 57. Algebraic solution. The equation is nonlinear, so make one side zero. This is already done, so factor out the GCF. x2 − 3x = 0 Original equation is nonlinear. x(x − 3) = 0 Factor out GCF. Use the zero product property to set both factors equal to zero, then solve the resulting equations. x=0 or x−3=0 x=3 Hence, the solutions are x = 0 and x = 3. Calculator solution. Load the left-hand side of the equation x2 − 3x = 0 into Y1 in the Y= menu, then select 6:ZStandard from the ZOOM menu to produce the following graph. Second Edition: 2012-2013 CHAPTER 6. FACTORING 362 Next, use the 2:zero utility from the CALC menu to ﬁnd the points of intersection. Report the results on your homework as follows. y y = x2 − 3x 10 −10 0 10 3 x −10 Hence, the solutions of x2 − 3x = 0 are x = 0 and x = 3. Note how these agree with the algebraic solution. 6.3 Factoring Trinomials I 1. We proceed as follows: i) Compare x2 + 7x − 18 with ax2 + bx + c and identify a = 1, b = 7, and c = −18. Note that the leading coeﬃcient is a = 1. ii) Calculate ac. Note that ac = (1)(−18), so ac = −18. iii) List all integer pairs whose product is ac = −18. 1, −18 2, −9 3, −6 Second Edition: 2012-2013 −1, 18 −2, 9 −3, 6 6.3. FACTORING TRINOMIALS I 363 iv) Circle the ordered pair whose sum is b = 7. 1, −18 2, −9 3, −6 −1, 18 −2, 9 −3, 6 v) Write the middle term as a sum of like terms using the boxed ordered pair. Then factor by grouping. x2 + 7x − 18 = x2 − 2x + 9x − 18 = x(x − 2) + 9(x − 2) = (x + 9)(x − 2) 3. We proceed as follows: i) Compare x2 − 10x + 9 with ax2 + bx + c and identify a = 1, b = −10, and c = 9. Note that the leading coeﬃcient is a = 1. ii) Calculate ac. Note that ac = (1)(9), so ac = 9. iii) List all integer pairs whose product is ac = 9. 1, 9 3, 3 −1, −9 −3, −3 iv) Circle the ordered pair whose sum is b = −10. 1, 9 3, 3 −1, −9 −3, −3 v) Write the middle term as a sum of like terms using the boxed ordered pair. Then factor by grouping. x2 − 10x + 9 = x2 − x − 9x + 9 = x(x − 1) − 9(x − 1) = (x − 9)(x − 1) 5. We proceed as follows: i) Compare x2 + 14x + 45 with ax2 + bx + c and identify a = 1, b = 14, and c = 45. Note that the leading coeﬃcient is a = 1. ii) Calculate ac. Note that ac = (1)(45), so ac = 45. iii) List all integer pairs whose product is ac = 45. 1, 45 3, 15 5, 9 −1, −45 −3, −15 −5, −9 Second Edition: 2012-2013 CHAPTER 6. FACTORING 364 iv) Circle the ordered pair whose sum is b = 14. 1, 45 3, 15 5, 9 −1, −45 −3, −15 −5, −9 v) Write the middle term as a sum of like terms using the boxed ordered pair. Then factor by grouping. x2 + 14x + 45 = x2 + 5x + 9x + 45 = x(x + 5) + 9(x + 5) = (x + 9)(x + 5) 7. Compare x2 − 16x + 39 with ax2 + bx + c and note that a = 1, b = −16, and c = 39. Calculate ac = (1)(39), so ac = 39. Start listing the integer pairs whose product is ac = 39, but be mindful that you need an integer pair whose sum is b = −16. 1, 39 −1, −39 3, 13 −3, −13 Note how we ceased listing ordered pairs the moment we found the pair we needed. Write the middle term as a sum of like terms using the boxed ordered pair. Then factor by grouping. x2 − 16x + 39 = x2 − 3x − 13x + 39 = x(x − 3) − 13(x − 3) = (x − 13)(x − 3) 9. Compare x2 − 26x + 69 with ax2 + bx + c and note that a = 1, b = −26, and c = 69. Calculate ac = (1)(69), so ac = 69. Start listing the integer pairs whose product is ac = 69, but be mindful that you need an integer pair whose sum is b = −26. 1, 69 −1, −69 3, 23 −3, −23 Note how we ceased listing ordered pairs the moment we found the pair we needed. Write the middle term as a sum of like terms using the boxed ordered pair. Then factor by grouping. x2 − 26x + 69 = x2 − 3x − 23x + 69 = x(x − 3) − 23(x − 3) = (x − 23)(x − 3) Second Edition: 2012-2013 6.3. FACTORING TRINOMIALS I 365 11. Compare x2 − 25x + 84 with ax2 + bx + c and note that a = 1, b = −25, and c = 84. Calculate ac = (1)(84), so ac = 84. Start listing the integer pairs whose product is ac = 84, but be mindful that you need an integer pair whose sum is b = −25. 1, 84 −1, −84 2, 42 −2, −42 3, 28 −3, −28 4, 21 −4, −21 Note how we ceased listing ordered pairs the moment we found the pair we needed. Write the middle term as a sum of like terms using the boxed ordered pair. Then factor by grouping. x2 − 25x + 84 = x2 − 4x − 21x + 84 = x(x − 4) − 21(x − 4) = (x − 21)(x − 4) 13. Compare x2 − 13x + 36 with ax2 + bx + c and note that a = 1, b = −13, and c = 36. Calculate ac = (1)(36), so ac = 36. Now can you think of an integer pair whose product is ac = 36 and whose sum is b = −13? For some, the pair just pops into their head: −4 and −9. “Drop” the pair in place and you are done. x2 − 13x + 36 = (x − 4)(x − 9) 15. Compare x2 + 10x + 21 with ax2 + bx + c and note that a = 1, b = 10, and c = 21. Calculate ac = (1)(21), so ac = 21. Now can you think of an integer pair whose product is ac = 21 and whose sum is b = 10? For some, the pair just pops into their head: 3 and 7. “Drop” the pair in place and you are done. x2 + 10x + 21 = (x + 3)(x + 7) 17. Compare x2 − 4x − 5 with ax2 + bx + c and note that a = 1, b = −4, and c = −5. Calculate ac = (1)(−5), so ac = −5. Now can you think of an integer pair whose product is ac = −5 and whose sum is b = −4? For some, the pair just pops into their head: 1 and −5. “Drop” the pair in place and you are done. x2 − 4x − 5 = (x + 1)(x − 5) Second Edition: 2012-2013 CHAPTER 6. FACTORING 366 19. Because there is a power of x larger than one, the equation is nonlinear. Make one side zero. x2 = −7x + 30 Original equation. 2 x + 7x = 30 Add 7x to both sides. 2 x + 7x − 30 = 0 Subtract 30 from both sides. Compare x2 +7x−30 with ax2 +bx+c and note that a = 1, b = 7 and c = −30. Note that the leading coeﬃcient is a 1. Calculate ac = (1)(−30) and list all integer pairs whose product is ac = −30. 1, −30 2, −15 3, −10 5, −6 −1, 30 −2, 15 −3, 10 −5, 6 Circle the ordered pair whose sum is b = 7. 1, −30 2, −15 3, −10 5, −6 −1, 30 −2, 15 −3, 10 −5, 6 Write the middle term as a sum of like terms using the boxed ordered pair. Then factor by grouping. x2 − 3x + 10x − 30 = 0 x(x − 3) + 10(x − 3) = 0 (x − 3)(x + 10) = 0 We have a product that equals zero. The zero product property tells us that at least one of the factors is zero. Either the ﬁrst factor is zero or the second factor is zero. x−3 = 0 x=3 or x + 10 = 0 x = −10 Thus, the solutions of x2 + 7x − 30 are x = 3 and x = −10. 21. Because there is a power of x larger than one, the equation is nonlinear. Make one side zero. x2 = −11x − 10 2 x + 11x = −10 2 x + 11x + 10 = 0 Second Edition: 2012-2013 Original equation. Add 11x to both sides. Add 10 to both sides. 6.3. FACTORING TRINOMIALS I 367 Compare x2 + 11x + 10 with ax2 + bx + c and note that a = 1, b = 11 and c = 10. Note that the leading coeﬃcient is a 1. Calculate ac = (1)(10) and list all integer pairs whose product is ac = 10. −1, −10 −2, −5 1, 10 2, 5 Circle the ordered pair whose sum is b = 11. −1, −10 −2, −5 1, 10 2, 5 Write the middle term as a sum of like terms using the boxed ordered pair. Then factor by grouping. x2 + x + 10x + 10 = 0 x(x + 1) + 10(x + 1) = 0 (x + 1)(x + 10) = 0 We have a product that equals zero. The zero product property tells us that at least one of the factors is zero. Either the ﬁrst factor is zero or the second factor is zero. x+1=0 or x + 10 = 0 x = −1 x = −10 Thus, the solutions of x2 + 11x + 10 are x = −1 and x = −10. 23. Because there is a power of x larger than one, the equation is nonlinear. Make one side zero. x2 = −15x − 50 Original equation. 2 x + 15x = −50 Add 15x to both sides. 2 x + 15x + 50 = 0 Add 50 to both sides. Compare x2 + 15x + 50 with ax2 + bx + c and note that a = 1, b = 15 and c = 50. Note that the leading coeﬃcient is a 1. Calculate ac = (1)(50) and list all integer pairs whose product is ac = 50. 1, 50 2, 25 5, 10 −1, −50 −2, −25 −5, −10 Circle the ordered pair whose sum is b = 15. 1, 50 2, 25 5, 10 −1, −50 −2, −25 −5, −10 Second Edition: 2012-2013 CHAPTER 6. FACTORING 368 Write the middle term as a sum of like terms using the boxed ordered pair. Then factor by grouping. x2 + 5x + 10x + 50 = 0 x(x + 5) + 10(x + 5) = 0 (x + 5)(x + 10) = 0 We have a product that equals zero. The zero product property tells us that at least one of the factors is zero. Either the ﬁrst factor is zero or the second factor is zero. x+5=0 x = −5 or x + 10 = 0 x = −10 Thus, the solutions of x2 + 15x + 50 are x = −5 and x = −10. 25. Because there is a power of x larger than one, the equation is nonlinear. Make one side zero. 60 = x2 + 11x Original equation. 2 0 = x + 11x − 60 Subtract 60 from both sides. Compare x2 + 11x − 60 with ax2 + bx + c and note that a = 1, b = 11 and c = −60. Note that the leading coeﬃcient is a 1. Calculate ac = (1)(−60) and begin listing all integer pairs whose product is ac = −60. Stop listing integer pairs when you ﬁnd and circle a pair whose sum is b = 11. 1, −60 2, −30 3, −20 4, −15 −1, 60 −2, 30 −3, 20 −4, 15 Write the middle term as a sum of like terms using the boxed ordered pair. Then factor by grouping. x2 − 4x + 15x − 60 = 0 x(x − 4) + 15(x − 4) = 0 (x − 4)(x + 15) = 0 We have a product that equals zero. The zero product property tells us that at least one of the factors is zero. Either the ﬁrst factor is zero or the second factor is zero. x−4 = 0 x=4 or x + 15 = 0 x = −15 Thus, the solutions of 60 = x2 + 11x are x = 4 and x = −15. Second Edition: 2012-2013 6.3. FACTORING TRINOMIALS I 369 27. Because there is a power of x larger than one, the equation is nonlinear. Make one side zero. −11 = x2 − 12x Original equation. 2 0 = x − 12x + 11 Add 11 to both sides. Compare x2 − 12x + 11 with ax2 + bx + c and note that a = 1, b = −12 and c = 11. Note that the leading coeﬃcient is a 1. Calculate ac = (1)(11) and begin listing all integer pairs whose product is ac = 11. Stop listing integer pairs when you ﬁnd and circle a pair whose sum is b = −12. −1, −11 1, 11 Write the middle term as a sum of like terms using the boxed ordered pair. Then factor by grouping. x2 − x − 11x + 11 = 0 x(x − 1) − 11(x − 1) = 0 (x − 1)(x − 11) = 0 We have a product that equals zero. The zero product property tells us that at least one of the factors is zero. Either the ﬁrst factor is zero or the second factor is zero. x−1=0 or x − 11 = 0 x=1 x = 11 Thus, the solutions of −11 = x2 − 12x are x = 1 and x = 11. 29. Because there is a power of x larger than one, the equation is nonlinear. Make one side zero. 56 = x2 + 10x Original equation. 2 0 = x + 10x − 56 Subtract 56 from both sides. Compare x2 + 10x − 56 with ax2 + bx + c and note that a = 1, b = 10 and c = −56. Note that the leading coeﬃcient is a 1. Calculate ac = (1)(−56) and begin listing all integer pairs whose product is ac = −56. Stop listing integer pairs when you ﬁnd and circle a pair whose sum is b = 10. 1, −56 2, −28 4, −14 −1, 56 −2, 28 −4, 14 Second Edition: 2012-2013 CHAPTER 6. FACTORING 370 Write the middle term as a sum of like terms using the boxed ordered pair. Then factor by grouping. x2 − 4x + 14x − 56 = 0 x(x − 4) + 14(x − 4) = 0 (x − 4)(x + 14) = 0 We have a product that equals zero. The zero product property tells us that at least one of the factors is zero. Either the ﬁrst factor is zero or the second factor is zero. x−4 = 0 x=4 or x + 14 = 0 x = −14 Thus, the solutions of 56 = x2 + 10x are x = 4 and x = −14. 31. Because there is a power of x larger than one, the equation is nonlinear. Make one side zero. x2 + 20 = −12x Original equation. 2 x + 12x + 20 = 0 Add 12x to both sides. Compare x2 + 12x + 20 with ax2 + bx + c and note that a = 1, b = 12, and c = 20. Calculate ac = (1)(20), so ac = 20. We need an integer pair whose product is ac = 20 and whose sum is b = 12. The integer pair 2 and 10 comes to mind. Drop this ordered pair in place. (x + 2)(x + 10) = 0 Factor. We have a product that equals zero. The zero product property tells us that at least one of the factors is zero. Either the ﬁrst factor is zero or the second factor is zero. x+2=0 x = −2 or x + 10 = 0 x = −10 Thus, the solutions of x2 + 20 = −12x are x = −2 and x = −10. 33. Because there is a power of x larger than one, the equation is nonlinear. Make one side zero. x2 − 36 = 9x 2 x − 9x − 36 = 0 Second Edition: 2012-2013 Original equation. Subtract 9x from both sides. 6.3. FACTORING TRINOMIALS I 371 Compare x2 − 9x − 36 with ax2 + bx + c and note that a = 1, b = −9, and c = −36. Calculate ac = (1)(−36), so ac = −36. We need an integer pair whose product is ac = −36 and whose sum is b = −9. The integer pair 3 and −12 comes to mind. Drop this ordered pair in place. (x + 3)(x − 12) = 0 Factor. We have a product that equals zero. The zero product property tells us that at least one of the factors is zero. Either the ﬁrst factor is zero or the second factor is zero. x+3=0 or x = −3 x − 12 = 0 x = 12 Thus, the solutions of x2 − 36 = 9x are x = −3 and x = 12. 35. Because there is a power of x larger than one, the equation is nonlinear. Make one side zero. x2 + 8 = −6x Original equation. 2 x + 6x + 8 = 0 Add 6x to both sides. Compare x2 + 6x + 8 with ax2 + bx + c and note that a = 1, b = 6, and c = 8. Calculate ac = (1)(8), so ac = 8. We need an integer pair whose product is ac = 8 and whose sum is b = 6. The integer pair 2 and 4 comes to mind. Drop this ordered pair in place. (x + 2)(x + 4) = 0 Factor. We have a product that equals zero. The zero product property tells us that at least one of the factors is zero. Either the ﬁrst factor is zero or the second factor is zero. x+2=0 x = −2 or x+4=0 x = −4 Thus, the solutions of x2 + 8 = −6x are x = −2 and x = −4. 37. Algebraic solution. The equation is nonlinear, so make one side zero by moving all terms containing x to one side of the equation. x2 = x + 12 x2 − x = 12 2 x − x − 12 = 0 The equation is nonlinear, so make one side zero. Subtract x from both sides. Subtract 12 from both sides. Second Edition: 2012-2013 CHAPTER 6. FACTORING 372 Note that ac = (1)(−12) = −12. The integer pair 3 and −4 gives a product of −12 and sums to −1, the coeﬃcient of x. Hence, we can “drop these numbers in place” to factor. (x + 3)(x − 4) = 0 Factor. Use the zero product property to set both factors equal to zero, then solve the resulting equations. x+3=0 or x = −3 x−4=0 x = −4 Hence, the solutions are x = −3 and x = 4. Calculator solution. Load each side of the equation x2 = x + 12 into Y1 and Y2 in the Y= menu, then select 6:ZStandard from the ZOOM menu to produce the following graph. We need both points of intersection to be visible in the viewing window. Adjust the WINDOW parameters as shown, then push the GRAPH button to produce the accompanying graph. Next, use the 5:intersect utility from the CALC menu to ﬁnd the points of intersection. Second Edition: 2012-2013 6.3. FACTORING TRINOMIALS I 373 Report the results on your homework as follows. y y = x2 30 y = x + 12 −10 −3 10 4 x −10 Hence, the solutions of x2 = x + 12 are x = −3 and x = 4. Note how these agree with the algebraic solution. 39. Algebraic solution. The equation is nonlinear, so make one side zero by moving all terms containing x to one side of the equation. x2 + 12 = 8x x2 − 8x + 12 = 0 The equation is nonlinear, so make one side zero. Subtract 8x from both sides. Note that ac = (1)(12) = 12. The integer pair −6 and −2 gives a product of 12 and sums to −8, the coeﬃcient of x. Hence, we can “drop these numbers in place” to factor. (x − 6)(x − 2) = 0 Factor. Use the zero product property to set both factors equal to zero, then solve the resulting equations. x−6=0 or x=6 x−2=0 x=2 Hence, the solutions are x = 6 and x = 2. Calculator solution. Load each side of the equation x2 + 12 = 8x into Y1 and Y2 in the Y= menu, then select 6:ZStandard from the ZOOM menu to produce the following graph. Second Edition: 2012-2013 374 CHAPTER 6. FACTORING We need both points of intersection to be visible in the viewing window. We know the graph of y = x2 + 12 is a parabola and if we substitute x = 0, we get y = 12, putting the y-intercept at (0, 12), so we need to elevate the top of the window. Adjust the WINDOW parameters as shown, then push the GRAPH button to produce the accompanying graph. Next, use the 5:intersect utility from the CALC menu to ﬁnd the points of intersection. Report the results on your homework as follows. Second Edition: 2012-2013 6.3. FACTORING TRINOMIALS I 375 y y = x2 + 12 y = 8x 70 −10 2 6 10 x −10 Hence, the solutions of x2 + 12 = 8x are x = 2 and x = 6. Note how these agree with the algebraic solution. 41. Algebraic solution. The equation is nonlinear, so make one side zero. This is already done, so use the ac-method to factor. Note that ac = (1)(−16) = −16 and the integer pair −8 and 2 has product −16 and adds to −6, the coefﬁcient of x. Hence, we can “drop” this pair in place to factor. x2 − 6x − 16 = 0 (x − 8)(x + 2) = 0 Use the zero product property to set both factors equal to zero, then solve the resulting equations. x−8=0 x=8 or x+2=0 x = −2 Hence, the solutions are x = 8 and x = −2. Calculator solution. Load the left-hand side of the equation x2 − 6x− 16 = 0 into Y1 in the Y= menu, then select 6:ZStandard from the ZOOM menu to produce the following graph. Second Edition: 2012-2013 CHAPTER 6. FACTORING 376 Both x-intercepts are visible, but we really should adjust the viewing window so that the vertex of the parabola is visible in the viewing window as well. Adjust the WINDOW parameters as shown, then push the GRAPH button to produce the accompanying graph. Next, use the 2:zero utility from the CALC menu to ﬁnd the points of intersection. Report the results on your homework as follows. y y = x2 − 6x − 16 10 −5 −2 8 15 x −30 Hence, the solutions of x2 − 6x − 16 = 0 are x = −2 and x = 8. Note how these agree with the algebraic solution. Second Edition: 2012-2013 6.3. FACTORING TRINOMIALS I 377 43. Algebraic solution. The equation is nonlinear, so make one side zero. This is already done, so use the ac-method to factor. Note that ac = (1)(−24) = −24 and the integer pair 12 and −2 has product −24 and adds to 10, the coeﬃcient of x. Hence, we can “drop” this pair in place to factor. x2 + 10x − 24 = 0 (x + 12)(x − 2) = 0 Use the zero product property to set both factors equal to zero, then solve the resulting equations. x + 12 = 0 or x = −12 x−2 = 0 x=2 Hence, the solutions are x = −12 and x = 2. Calculator solution. Load the left-hand side of the equation x2 +10x−24 = 0 into Y1 in the Y= menu, then select 6:ZStandard from the ZOOM menu to produce the following graph. We know that y = x2 + 10x − 24 = 0 is a parabola that opens upward, but only one x-intercept is visible. We need to move the viewing window a bit to the left to see the second x-intercept, and also move it downward so that the vertex of the parabola is visible in the viewing window as well. Adjust the WINDOW parameters as shown, then push the GRAPH button to produce the accompanying graph. Next, use the 2:zero utility from the CALC menu to ﬁnd the points of intersection. Second Edition: 2012-2013 CHAPTER 6. FACTORING 378 Report the results on your homework as follows. y y = x2 + 10x − 24 10 −15 −12 2 5 x −60 Hence, the solutions of x2 + 10x − 24 = 0 are x = −12 and x = 2. Note how these agree with the algebraic solution. 6.4 Factoring Trinomials II 1. We proceed as follows: i) Compare 6x2 + 13x − 5 with ax2 + bx + c and identify a = 6, b = 13, and c = −5. Note that the leading coeﬃcient is a = 6, so this case is not a “drop in place” situation. ii) Calculate ac. Note that ac = (6)(−5), so ac = −30. iii) List all integer pairs whose product is ac = −30. 1, −30 2, −15 3, −10 5, −6 Second Edition: 2012-2013 −1, 30 −2, 15 −3, 10 −5, 6 6.4. FACTORING TRINOMIALS II 379 iv) Circle the ordered pair whose sum is b = 13. 1, −30 2, −15 3, −10 5, −6 −1, 30 −2, 15 −3, 10 −5, 6 v) If we try to “drop in place”, (x − 2)(x + 15) = 6x2 + 13x − 5. Right oﬀ the bat, the product of the terms in the “First” position does not equal 6x2 . Instead, we must break up the middle term of 6x2 + 13x − 5 into a sum of like terms using our circled pair of integers −2 and 15. 6x2 + 13x − 5 = 6x2 − 2x + 15x − 5 Now we factor by grouping. Factor 2x out of the ﬁrst two terms and 5 out of the second two terms. = 2x (3x − 1) + 5 (3x − 1) Now we can factor out (3x − 1). = (2x + 5)(3x − 1) 3. We proceed as follows: i) Compare 4x2 − x − 3 with ax2 + bx + c and identify a = 4, b = −1, and c = −3. Note that the leading coeﬃcient is a = 4, so this case is not a “drop in place” situation. ii) Calculate ac. Note that ac = (4)(−3), so ac = −12. iii) List all integer pairs whose product is ac = −12. 1, −12 2, −6 3, −4 −1, 12 −2, 6 −3, 4 iv) Circle the ordered pair whose sum is b = −1. 1, −12 2, −6 3, −4 −1, 12 −2, 6 −3, 4 v) If we try to “drop in place”, (x + 3)(x − 4) = 4x2 − x − 3. Right oﬀ the bat, the product of the terms in the “First” position does not equal 4x2 . Second Edition: 2012-2013 CHAPTER 6. FACTORING 380 Instead, we must break up the middle term of 4x2 − x − 3 into a sum of like terms using our circled pair of integers 3 and −4. 4x2 − x − 3 = 4x2 + 3x − 4x − 3 Now we factor by grouping. Factor x out of the ﬁrst two terms and −1 out of the second two terms. = x (4x + 3) − 1 (4x + 3) Now we can factor out (4x + 3). = (x − 1)(4x + 3) 5. We proceed as follows: i) Compare 3x2 + 19x + 28 with ax2 + bx + c and identify a = 3, b = 19, and c = 28. Note that the leading coeﬃcient is a = 3, so this case is not a “drop in place” situation. ii) Calculate ac. Note that ac = (3)(28), so ac = 84. iii) List all integer pairs whose product is ac = 84. 1, 84 2, 42 3, 28 4, 21 6, 14 7, 12 −1, −84 −2, −42 −3, −28 −4, −21 −6, −14 −7, −12 iv) Circle the ordered pair whose sum is b = 19. 1, 84 2, 42 3, 28 4, 21 6, 14 7, 12 −1, −84 −2, −42 −3, −28 −4, −21 −6, −14 −7, −12 v) If we try to “drop in place”, (x + 7)(x + 12) = 3x2 + 19x + 28. Right oﬀ the bat, the product of the terms in the “First” position does not equal 3x2 . Instead, we must break up the middle term of 3x2 + 19x + 28 into a sum of like terms using our circled pair of integers 7 and 12. 3x2 + 19x + 28 = 3x2 + 7x + 12x + 28 Second Edition: 2012-2013 6.4. FACTORING TRINOMIALS II 381 Now we factor by grouping. Factor x out of the ﬁrst two terms and 4 out of the second two terms. = x (3x + 7) + 4 (3x + 7) Now we can factor out (3x + 7). = (x + 4)(3x + 7) 7. Compare 12x2 − 23x + 5 with ax2 + bx + c and note that a = 12, b = −23, and c = 5. Calculate ac = (12)(5), so ac = 60. Start listing the integer pairs whose product is ac = 60, but be mindful that you need an integer pair whose sum is b = −23. Note how we ceased listing ordered pairs the moment we found the pair we needed. 1, 60 2, 30 3, 20 −1, −60 −2, −30 −3, −20 If we try to “drop in place”, (x − 3)(x − 20) = 12x2 − 23x + 5. Right oﬀ the bat, the product of the terms in the “First” position does not equal 12x2 . Instead, we must break up the middle term of 12x2 − 23x + 5 into a sum of like terms using our circled pair of integers −3 and −20. 12x2 − 23x + 5 = 12x2 − 3x − 20x + 5 Now we factor by grouping. Factor 3x out of the ﬁrst two terms and −5 out of the second two terms. = 3x (4x − 1) − 5 (4x − 1) Now we can factor out (4x − 1). = (3x − 5)(4x − 1) 9. Compare 6x2 + 17x + 7 with ax2 + bx + c and note that a = 6, b = 17, and c = 7. Calculate ac = (6)(7), so ac = 42. Start listing the integer pairs whose product is ac = 42, but be mindful that you need an integer pair whose sum is b = 17. Note how we ceased listing ordered pairs the moment we found the pair we needed. 1, 42 −1, −42 2, 21 −2, −21 3, 14 If we try to “drop in place”, (x + 3)(x + 14) = 6x2 + 17x + 7. Right oﬀ the bat, the product of the terms in the “First” position does not equal 6x2 . Instead, Second Edition: 2012-2013 CHAPTER 6. FACTORING 382 we must break up the middle term of 6x2 + 17x + 7 into a sum of like terms using our circled pair of integers 3 and 14. 6x2 + 17x + 7 = 6x2 + 14x + 3x + 7 Now we factor by grouping. Factor 2x out of the ﬁrst two terms and 1 out of the second two terms. = 2x (3x + 7) + 1 (3x + 7) Now we can factor out (3x + 7). = (2x + 1)(3x + 7) 11. Compare 3x2 + 4x − 32 with ax2 + bx + c and note that a = 3, b = 4, and c = −32. Calculate ac = (3)(−32), so ac = −96. Start listing the integer pairs whose product is ac = −96, but be mindful that you need an integer pair whose sum is b = 4. Note how we ceased listing ordered pairs the moment we found the pair we needed. 1, −96 2, −48 3, −32 4, −24 6, −16 8, −12 −1, 96 −2, 48 −3, 32 −4, 24 −6, 16 −8, 12 If we try to “drop in place”, (x − 8)(x + 12) = 3x2 + 4x − 32. Right oﬀ the bat, the product of the terms in the “First” position does not equal 3x2 . Instead, we must break up the middle term of 3x2 + 4x − 32 into a sum of like terms using our circled pair of integers −8 and 12. 3x2 + 4x − 32 = 3x2 − 8x + 12x − 32 Now we factor by grouping. Factor x out of the ﬁrst two terms and 4 out of the second two terms. = x (3x − 8) + 4 (3x − 8) Now we can factor out (3x − 8). = (x + 4)(3x − 8) Second Edition: 2012-2013 6.4. FACTORING TRINOMIALS II 383 13. Compare 3x2 + 28x + 9 with ax2 + bx + c and note that a = 3, b = 28, and c = 9. Calculate ac = (3)(9), so ac = 27. We need an integer pair whose product is ac = 27 and whose sum is b = 28. The integer pair 1 and 27 comes to mind. If we try to “drop in place”, (x + 1)(x + 27) = 3x2 + 28x + 9. Right oﬀ the bat, the product of the terms in the “First” position does not equal 3x2 . Instead, we must break up the middle term of 3x2 + 28x + 9 into a sum of like terms using the integer pair 1 and 27. 3x2 + 28x + 9 = 3x2 + x + 27x + 9 Now we factor by grouping. Factor x out of the ﬁrst two terms and 9 out of the second two terms. = x (3x + 1) + 9 (3x + 1) Now we can factor out (3x + 1). = (x + 9)(3x + 1) 15. Compare 4x2 − 21x + 5 with ax2 + bx + c and note that a = 4, b = −21, and c = 5. Calculate ac = (4)(5), so ac = 20. We need an integer pair whose product is ac = 20 and whose sum is b = −21. The integer pair −1 and −20 comes to mind. If we try to “drop in place”, (x − 1)(x − 20) = 4x2 − 21x + 5. Right oﬀ the bat, the product of the terms in the “First” position does not equal 4x2 . Instead, we must break up the middle term of 4x2 − 21x + 5 into a sum of like terms using the integer pair −1 and −20. 4x2 − 21x + 5 = 4x2 − x − 20x + 5 Now we factor by grouping. Factor x out of the ﬁrst two terms and −5 out of the second two terms. = x (4x − 1) − 5 (4x − 1) Now we can factor out (4x − 1). = (x − 5)(4x − 1) 17. Compare 6x2 − 11x − 7 with ax2 + bx + c and note that a = 6, b = −11, and c = −7. Calculate ac = (6)(−7), so ac = −42. We need an integer pair whose product is ac = −42 and whose sum is b = −11. The integer pair 3 and −14 comes to mind. Second Edition: 2012-2013 CHAPTER 6. FACTORING 384 If we try to “drop in place”, (x + 3)(x − 14) = 6x2 − 11x − 7. Right oﬀ the bat, the product of the terms in the “First” position does not equal 6x2 . Instead, we must break up the middle term of 6x2 − 11x − 7 into a sum of like terms using the integer pair 3 and −14. 6x2 − 11x − 7 = 6x2 + 3x − 14x − 7 Now we factor by grouping. Factor 3x out of the ﬁrst two terms and −7 out of the second two terms. = 3x (2x + 1) − 7 (2x + 1) Now we can factor out (2x + 1). = (3x − 7)(2x + 1) 19. Note that the GCF of 16x5 , −36x4 , and 14x3 is 2x3 . Factor out this GCF. 16x5 − 36x4 + 14x3 = 2x3 · 8x2 − 2x3 · 18x + 2x3 · 7 = 2x3 (8x2 − 18x + 7) Next, compare 8x2 − 18x + 7 with ax2 + bx + c and note that a = 8, b = −18, and c = 7. Start listing the integer pairs whose product is ac = (8)(7), or ac = 56, but be mindful that you need an integer pair whose sum is b = −18. 1, 56 2, 28 4, 14 −1, −56 −2, −28 −4, −14 Break up the middle term of 8x2 − 18x + 7 into a sum of like terms using our circled pair of integers −4 and −14. 2x3 (8x2 − 18x + 7) = 2x3 (8x2 − 14x − 4x + 7) Now we factor by grouping. Factor 2x out of the ﬁrst two terms and −1 out of the second two terms. = 2x3 2x (4x − 7) − 1 (4x − 7) Now we can factor out (4x − 7). = 2x3 (2x − 1)(4x − 7) Second Edition: 2012-2013 6.4. FACTORING TRINOMIALS II 385 21. Note that the GCF of 36x4 , −75x3 , and 21x2 is 3x2 . Factor out this GCF. 36x4 − 75x3 + 21x2 = 3x2 · 12x2 − 3x2 · 25x + 3x2 · 7 = 3x2 (12x2 − 25x + 7) Next, compare 12x2 − 25x + 7 with ax2 + bx + c and note that a = 12, b = −25, and c = 7. Start listing the integer pairs whose product is ac = (12)(7), or ac = 84, but be mindful that you need an integer pair whose sum is b = −25. −1, −84 −2, −42 −3, −28 −4, −21 1, 84 2, 42 3, 28 4, 21 Break up the middle term of 12x2 − 25x + 7 into a sum of like terms using our circled pair of integers −4 and −21. 3x2 (12x2 − 25x + 7) = 3x2 (12x2 − 21x − 4x + 7) Now we factor by grouping. Factor 3x out of the ﬁrst two terms and −1 out of the second two terms. = 3x2 3x (4x − 7) − 1 (4x − 7) Now we can factor out (4x − 7). = 3x2 (3x − 1)(4x − 7) 23. Note that the GCF of 6x4 , −33x3 , and 42x2 is 3x2 . Factor out this GCF. 6x4 − 33x3 + 42x2 = 3x2 · 2x2 − 3x2 · 11x + 3x2 · 14 = 3x2 (2x2 − 11x + 14) Next, compare 2x2 − 11x + 14 with ax2 + bx + c and note that a = 2, b = −11, and c = 14. Start listing the integer pairs whose product is ac = (2)(14), or ac = 28, but be mindful that you need an integer pair whose sum is b = −11. 1, 28 2, 14 4, 7 −1, −28 −2, −14 −4, −7 Break up the middle term of 2x2 − 11x + 14 into a sum of like terms using our circled pair of integers −4 and −7. 3x2 (2x2 − 11x + 14) = 3x2 (2x2 − 7x − 4x + 14) Second Edition: 2012-2013 CHAPTER 6. FACTORING 386 Now we factor by grouping. Factor x out of the ﬁrst two terms and −2 out of the second two terms. = 3x2 x (2x − 7) − 2 (2x − 7) Now we can factor out (2x − 7). = 3x2 (x − 2)(2x − 7) 25. Note that the GCF of 16x4 , −36x3 , and −36x2 is 4x2 . Factor out this GCF. 16x4 − 36x3 − 36x2 = 4x2 · 4x2 − 4x2 · 9x − 4x2 · 9 = 4x2 (4x2 − 9x − 9) Next, compare 4x2 − 9x − 9 with ax2 + bx + c and note that a = 4, b = −9, and c = −9. Start listing the integer pairs whose product is ac = (4)(−9), or ac = −36, but be mindful that you need an integer pair whose sum is b = −9. 1, −36 2, −18 3, −12 −1, 36 −2, 18 Break up the middle term of 4x2 − 9x − 9 into a sum of like terms using our circled pair of integers 3 and −12. 4x2 (4x2 − 9x − 9) = 4x2 (4x2 + 3x − 12x − 9) Now we factor by grouping. Factor x out of the ﬁrst two terms and −3 out of the second two terms. = 4x2 x (4x + 3) − 3 (4x + 3) Now we can factor out (4x + 3). = 4x2 (x − 3)(4x + 3) 27. Because there is a power of x larger than one, the equation is nonlinear. Make one side zero. 4x2 = −x + 18 2 4x + x = 18 2 4x + x − 18 = 0 Second Edition: 2012-2013 Original equation. Add x to both sides. Subtract 18 from both sides. 6.4. FACTORING TRINOMIALS II 387 Compare 4x2 + x − 18 with ax2 + bx + c and note that a = 4, b = 1, and c = −18. Calculate ac = (4)(−18), so ac = −72. We need an integer pair whose product is ac = −72 and whose sum is b = 1. The integer pair −8 and 9 comes to mind. Break up the middle term of 4x2 + x − 18 into a sum of like terms using the integer pair −8 and 9. 4x2 + 9x − 8x − 18 = 0 x (4x + 9) − 2 (4x + 9) = 0 x = 9x − 8x Factor by grouping. (x − 2)(4x + 9) = 0 Factor out 4x + 9. We have a product that equals zero. Use the zero product property to complete the solution. x−2=0 or 4x + 9 = 0 4x = −9 9 x=− 4 x=2 Thus, the solutions of 4x2 = −x + 18 are x = 2 and x = −9/4. 29. Because there is a power of x larger than one, the equation is nonlinear. Make one side zero. 3x2 + 16 = −14x Original equation. 2 3x + 14x + 16 = 0 Add 14x to both sides. Compare 3x2 + 14x + 16 with ax2 + bx + c and note that a = 3, b = 14, and c = 16. Calculate ac = (3)(16), so ac = 48. We need an integer pair whose product is ac = 48 and whose sum is b = 14. The integer pair 6 and 8 comes to mind. Break up the middle term of 3x2 + 14x + 16 into a sum of like terms using the integer pair 6 and 8. 3x2 + 8x + 6x + 16 = 0 x (3x + 8) + 2 (3x + 8) = 0 14x = 8x + 6x Factor by grouping. (x + 2)(3x + 8) = 0 Factor out 3x + 8. We have a product that equals zero. Use the zero product property to complete the solution. x+2=0 x = −2 or 3x + 8 = 0 3x = −8 8 x=− 3 Thus, the solutions of 3x2 + 16 = −14x are x = −2 and x = −8/3. Second Edition: 2012-2013 CHAPTER 6. FACTORING 388 31. Because there is a power of x larger than one, the equation is nonlinear. Make one side zero. 3x2 + 30 = 23x Original equation. 2 3x − 23x + 30 = 0 Subtract 23x from both sides. Compare 3x2 − 23x + 30 with ax2 + bx + c and note that a = 3, b = −23, and c = 30. Calculate ac = (3)(30), so ac = 90. We need an integer pair whose product is ac = 90 and whose sum is b = −23. The integer pair −5 and −18 comes to mind. Break up the middle term of 3x2 − 23x + 30 into a sum of like terms using the integer pair −5 and −18. 3x2 − 5x − 18x + 30 = 0 x (3x − 5) − 6 (3x − 5) = 0 −23x = −5x − 18x Factor by grouping. (x − 6)(3x − 5) = 0 Factor out 3x − 5. We have a product that equals zero. Use the zero product property to complete the solution. x−6=0 x=6 3x − 5 = 0 3x = 5 5 x= 3 Thus, the solutions of 3x2 + 30 = 23x are x = 6 and x = 5/3. or 33. Because there is a power of x larger than one, the equation is nonlinear. Make one side zero. −7x − 3 = −6x2 Original equation. 2 Add 6x2 to both sides. 6x − 7x − 3 = 0 Compare 6x2 − 7x − 3 with ax2 + bx + c and note that a = 6, b = −7, and c = −3. Calculate ac = (6)(−3), so ac = −18. We need an integer pair whose product is ac = −18 and whose sum is b = −7. The integer pair 2 and −9 comes to mind. Break up the middle term of 6x2 − 7x − 3 into a sum of like terms using the integer pair 2 and −9. 6x2 − 9x + 2x − 3 = 0 −7x = −9x + 2x 3x (2x − 3) + 1 (2x − 3) = 0 (3x + 1)(2x − 3) = 0 Factor by grouping. Factor out 2x − 3. We have a product that equals zero. Use the zero product property to complete the solution. 3x + 1 = 0 3x = −1 1 x=− 3 Second Edition: 2012-2013 or 2x − 3 = 0 2x = 3 3 x= 2 6.4. FACTORING TRINOMIALS II 389 Thus, the solutions of −7x − 3 = −6x2 are x = −1/3 and x = 3/2. 35. Because there is a power of x larger than one, the equation is nonlinear. Make one side zero. 26x − 9 = −3x2 Original equation. 2 Add 3x2 to both sides. 3x + 26x − 9 = 0 Compare 3x2 + 26x − 9 with ax2 + bx + c and note that a = 3, b = 26, and c = −9. Calculate ac = (3)(−9), so ac = −27. We need an integer pair whose product is ac = −27 and whose sum is b = 26. The integer pair −1 and 27 comes to mind. Break up the middle term of 3x2 + 26x − 9 into a sum of like terms using the integer pair −1 and 27. 3x2 − x + 27x − 9 = 0 x (3x − 1) + 9 (3x − 1) = 0 26x = −x + 27x Factor by grouping. (x + 9)(3x − 1) = 0 Factor out 3x − 1. We have a product that equals zero. Use the zero product property to complete the solution. x+9=0 x = −9 or 3x − 1 = 0 3x = 1 1 x= 3 Thus, the solutions of 26x − 9 = −3x2 are x = −9 and x = 1/3. 37. Because there is a power of x larger than one, the equation is nonlinear. Make one side zero. 6x2 = −25x + 9 2 6x + 25x = 9 2 6x + 25x − 9 = 0 Original equation. Add 25x to both sides. Subtract 9 from both sides. Compare 6x2 + 25x − 9 with ax2 + bx + c and note that a = 6, b = 25, and c = −9. Calculate ac = (6)(−9), so ac = −54. We need an integer pair whose product is ac = −54 and whose sum is b = 25. The integer pair −2 and 27 comes to mind. Break up the middle term of 6x2 + 25x − 9 into a sum of like terms using the integer pair −2 and 27. 6x2 + 27x − 2x − 9 = 0 3x (2x + 9) − 1 (2x + 9) = 0 (3x − 1)(2x + 9) = 0 25x = 27x − 2x Factor by grouping. Factor out 2x + 9. Second Edition: 2012-2013 CHAPTER 6. FACTORING 390 We have a product that equals zero. Use the zero product property to complete the solution. 3x − 1 = 0 or 2x + 9 = 0 2x = −9 9 x=− 2 3x = 1 1 x= 3 Thus, the solutions of 6x2 = −25x + 9 are x = 1/3 and x = −9/2. 39. Algebraic solution. The equation is nonlinear, so make one side zero. That’s already done, so use the ac-method to factor. Note that ac = (2)(−5) = −10 and the integer pair 1 and −10 has product −10 and sum −9, the coeﬃcient of x. Split the middle term up using this pair. 2x2 − 9x − 5 = 0 2x2 + x − 10x − 5 = 0 Factor by grouping. x(2x + 1) − 5(2x + 1) = 0 (x − 5)(2x + 1) = 0 Use the zero product property to set both factors equal to zero, then solve the resulting equations. x−5=0 or 2x + 1 = 0 x=5 x=− 1 2 Hence, the solutions are x = 5 and x = −1/2. Calculator solution. Load the left-hand side of the equation 2x2 − 9x− 5 = 0 into Y1 in the Y= menu, then select 6:ZStandard from the ZOOM menu to produce the following graph. Both x-intercepts are visible in the viewing window, but we really should adjust the WINDOW parameters so that the vertex of the parabola is visible in the viewing window. Adjust the WINDOW parameters as shown, then push the GRAPH button to produce the accompanying graph. Second Edition: 2012-2013 6.4. FACTORING TRINOMIALS II 391 Next, use the 2:zero utility from the CALC menu to ﬁnd the x-intercepts of the graph. Report the results on your homework as follows. y y = 2x2 − 9x − 5 20 −10 −0.5 5 10 x −20 Hence, the solutions of 2x2 − 9x − 5 = 0 are x = −0.5 and x = 5. Note how these agree with the algebraic solution, especially when you note that −0.5 = −1/2. 41. Algebraic solution. The equation is nonlinear, so make one side zero. That’s already done, so use the ac-method to factor. Note that ac = (4)(−15) = Second Edition: 2012-2013 CHAPTER 6. FACTORING 392 −60 and the integer pair 3 and −20 has product −60 and sum −17, the coefﬁcient of x. Split the middle term up using this pair. 4x2 − 17x − 15 = 0 4x2 + 3x − 20x − 15 = 0 Factor by grouping. x(4x + 3) − 5(4x + 3) = 0 (x − 5)(4x + 3) = 0 Use the zero product property to set both factors equal to zero, then solve the resulting equations. x−5=0 or 4x + 3 = 0 x=5 x=− 3 4 Hence, the solutions are x = 5 and x = −3/4. Calculator solution. Load the left-hand side of the equation 4x2 −17x−15 = 0 into Y1 in the Y= menu, then select 6:ZStandard from the ZOOM menu to produce the following graph. Both x-intercepts are visible in the viewing window, but we really should adjust the WINDOW parameters so that the vertex of the parabola is visible in the viewing window. Adjust the WINDOW parameters as shown, then push the GRAPH button to produce the accompanying graph. Next, use the 2:zero utility from the CALC menu to ﬁnd the x-intercepts of the graph. Second Edition: 2012-2013 6.4. FACTORING TRINOMIALS II 393 Report the results on your homework as follows. y y = 4x2 − 17x − 15 50 −10 −0.75 5 10 x −50 Hence, the solutions of 4x2 − 17x − 15 = 0 are x = −0.75 and x = 5. Note how these agree with the algebraic solution, especially when you note that −0.75 = −3/4. 43. Algebraic solution. The equation is nonlinear, so make one side zero. Subtract 3x2 and 20x from both sides. 2x3 = 3x2 + 20x 2x3 − 3x2 − 20x = 0 Factor out the GCF. x(2x2 − 3x − 20) = 0 Note that ac = (2)(−20) = −40 and the integer pair 5 and −8 have product −40 and sum −3, the coeﬃcient of x. Use this pair to break up the middle term. x(2x2 + 5x − 8x − 20) = 0 Second Edition: 2012-2013 CHAPTER 6. FACTORING 394 Factor by grouping. x(x(2x + 5) − 4(2x + 5)) = 0 x(x − 4)(2x + 5) = 0 Use the zero product property to set all three factors equal to zero, then solve the resulting equations. x=0 or x−4=0 or 2x + 5 = 0 x=4 x=− 5 2 Hence, the solutions are x = 0, x = 4, and x = −5/2. Calculator solution. Load the left-hand side of the equation 2x3 −3x2 −20x = 0 into Y1 in the Y= menu, then select 6:ZStandard from the ZOOM menu to produce the following graph. All three x-intercepts are visible in the viewing window, but we really should adjust the WINDOW parameters so that the turning points of the parabola are visible in the viewing window. Adjust the WINDOW parameters as shown, then push the GRAPH button to produce the accompanying graph. Next, use the 2:zero utility from the CALC menu to ﬁnd the x-intercepts of the graph. Second Edition: 2012-2013 6.4. FACTORING TRINOMIALS II 395 Report the results on your homework as follows. y y = 2x3 − 3x2 − 20x 50 −10 −2.5 0 4 10 x −50 Hence, the solutions of 2x3 = 3x2 + 20x are x = −2.5, x = 0, and x = 4. Note how these agree with the algebraic solution, especially when you note that −2.5 = −5/2. 45. Algebraic solution. The equation is nonlinear, so make one side zero. Subtract 24x from both sides. 10x3 + 34x2 = 24x 10x3 + 34x2 − 24x = 0 Factor out the GCF. 2x(5x2 + 17x − 12) = 0 Second Edition: 2012-2013 CHAPTER 6. FACTORING 396 Note that ac = (5)(−12) = −60 and the integer pair −3 and 20 have product −60 and sum 17, the coeﬃcient of x. Use this pair to break up the middle term. 2x(5x2 − 3x + 20x − 12) = 0 Factor by grouping. 2x(x(5x − 3) + 4(5x − 3)) = 0 2x(x + 4)(5x − 3) = 0 Use the zero product property to set all three factors equal to zero, then solve the resulting equations. 2x = 0 or x=0 x+4=0 or x = −4 5x − 3 = 0 3 x= 5 Hence, the solutions are x = 0, x = −4, and x = 3/5. Calculator solution. Load the left-hand side of the equation 10x3 + 34x2 − 24x = 0 into Y1 in the Y= menu, then select 6:ZStandard from the ZOOM menu to produce the following graph. All three x-intercepts are visible in the viewing window, but we really should adjust the WINDOW parameters so that the turning points of the parabola are visible in the viewing window. Adjust the WINDOW parameters as shown, then push the GRAPH button to produce the accompanying graph. Next, use the 2:zero utility from the CALC menu to ﬁnd the x-intercepts of the graph. Second Edition: 2012-2013 6.5. SPECIAL FORMS 397 Report the results on your homework as follows. y y = 10x3 + 34x2 − 24x 150 −10 −4 0 0.6 10 x −50 Hence, the solutions of 10x3 + 34x2 = 24x are x = −4, x = 0, and x = 0.6. Note how these agree with the algebraic solution, especially when you note that 0.6 = 3/5. 6.5 Special Forms 1. Using the pattern (a − b)2 = a2 − 2ab + b2 , we can expand (8r − 3t)2 as follows: (8r − 3t)2 = (8r)2 − 2(8r)(3t) + (3t)2 = 64r2 − 48rt + 9t2 Second Edition: 2012-2013 CHAPTER 6. FACTORING 398 Note how we square the ﬁrst and second terms, then produce the middle term of our answer by multiplying the ﬁrst and second terms and doubling. 3. Using the pattern (a + b)2 = a2 + 2ab + b2 , we can expand (4a + 7b)2 as follows: (4a + 7b)2 = (4a)2 + 2(4a)(7b) + (7b)2 = 16a2 + 56ab + 49b2 Note how we square the ﬁrst and second terms, then produce the middle term of our answer by multiplying the ﬁrst and second terms and doubling. 5. Using the pattern (a − b)2 = a2 − 2ab + b2 , we can expand (s3 − 9)2 as follows: (s3 − 9)2 = (s3 )2 − 2(s3 )(9) + (9)2 = s6 − 18s3 + 81 Note how we square the ﬁrst and second terms, then produce the middle term of our answer by multiplying the ﬁrst and second terms and doubling. 7. Using the pattern (a + b)2 = a2 + 2ab + b2 , we can expand (s2 + 6t2 )2 as follows: (s2 + 6t2 )2 = (s2 )2 + 2(s2 )(6t2 ) + (6t2 )2 = s4 + 12s2 t2 + 36t4 Note how we square the ﬁrst and second terms, then produce the middle term of our answer by multiplying the ﬁrst and second terms and doubling. 9. In the trinomial 25s2 + 60st + 36t2, note that (5s)2 = 25s2 and (6t)2 = 36t2 . Hence, the ﬁrst and last terms are perfect squares. Taking the square roots, we suspect that 25s2 + 60st + 36t2 factors as follows: 25s2 + 60st + 36t2 = (5s + 6t)2 However, we must check to see if the middle term is correct. Multiply 5s and 6t, then double: 2(5s)(6t) = 60st. Thus, the middle term is correct and we have the correct factorization of 25s2 + 60st + 36t2 . Second Edition: 2012-2013 6.5. SPECIAL FORMS 399 11. In the trinomial 36v 2 − 60vw + 25w2 , note that (6v)2 = 36v 2 and (5w)2 = 25w2 . Hence, the ﬁrst and last terms are perfect squares. Taking the square roots, we suspect that 36v 2 − 60vw + 25w2 factors as follows: 36v 2 − 60vw + 25w2 = (6v − 5w)2 However, we must check to see if the middle term is correct. Multiply 6v and 5w, then double: 2(6v)(5w) = 60vw. Thus, the middle term is correct and we have the correct factorization of 36v 2 − 60vw + 25w2 . 13. In the trinomial a4 +18a2 b2 +81b4 , note that (a2 )2 = a4 and (9b2 )2 = 81b4 . Hence, the ﬁrst and last terms are perfect squares. Taking the square roots, we suspect that a4 + 18a2 b2 + 81b4 factors as follows: a4 + 18a2 b2 + 81b4 = (a2 + 9b2 )2 However, we must check to see if the middle term is correct. Multiply a2 and 9b2 , then double: 2(a2 )(9b2 ) = 18a2 b2 . Thus, the middle term is correct and we have the correct factorization of a4 + 18a2 b2 + 81b4 . 15. In the trinomial 49s4 − 28s2 t2 + 4t4 , note that (7s2 )2 = 49s4 and (2t2 )2 = 4t4 . Hence, the ﬁrst and last terms are perfect squares. Taking the square roots, we suspect that 49s4 − 28s2 t2 + 4t4 factors as follows: 49s4 − 28s2 t2 + 4t4 = (7s2 − 2t2 )2 However, we must check to see if the middle term is correct. Multiply 7s2 and 2t2 , then double: 2(7s2 )(2t2 ) = 28s2 t2 . Thus, the middle term is correct and we have the correct factorization of 49s4 − 28s2 t2 + 4t4 . 17. In the trinomial 49b6 − 112b3 + 64, note that (7b3 )2 = 49b6 and (8)2 = 64. Hence, the ﬁrst and last terms are perfect squares. Taking the square roots, we suspect that 49b6 − 112b3 + 64 factors as follows: 49b6 − 112b3 + 64 = (7b3 − 8)2 However, we must check to see if the middle term is correct. Multiply 7b3 and 8, then double: 2(7b3 )(8) = 112b3. Thus, the middle term is correct and we have the correct factorization of 49b6 − 112b3 + 64. 19. In the trinomial 49r6 + 112r3 + 64, note that (7r3 )2 = 49r6 and (8)2 = 64. Hence, the ﬁrst and last terms are perfect squares. Taking the square roots, we suspect that 49r6 + 112r3 + 64 factors as follows: 49r6 + 112r3 + 64 = (7r3 + 8)2 However, we must check to see if the middle term is correct. Multiply 7r3 and 8, then double: 2(7r3 )(8) = 112r3 . Thus, the middle term is correct and we have the correct factorization of 49r6 + 112r3 + 64. Second Edition: 2012-2013 CHAPTER 6. FACTORING 400 21. 23. 25. In the trinomial −48b3 + 120b2 − 75b, we note that the GCF of 48b3 , 120b2, and 75b is 3b. We ﬁrst factor out 3b. −48b3 + 120b2 − 75b = 3b(−16b2 + 40b − 25) However, the ﬁrst and third terms of −16b2 + 40b − 25 are negative, and thus are not perfect squares. Let’s begin again, this time factoring out −3b. −48b3 + 120b2 − 75b = −3b(16b2 − 40b + 25) This time the ﬁrst and third terms of 16b2 − 40b + 25 are perfect squares. We take their square roots and write: = −3b(4b − 5)2 We must check that our middle term is correct. Because 2(4b)(5) = 40b, we do have a perfect square trinomial and our result is correct. 27. In the trinomial −5u5 − 30u4 − 45u3, we note that the GCF of 5u5 , 30u4, and 45u3 is 5u3 . We ﬁrst factor out 5u3 . −5u5 − 30u4 − 45u3 = 5u3 (−u2 − 6u − 9) However, the ﬁrst and third terms of −u2 − 6u − 9 are negative, and thus are not perfect squares. Let’s begin again, this time factoring out −5u3 . −5u5 − 30u4 − 45u3 = −5u3 (u2 + 6u + 9) This time the ﬁrst and third terms of u2 + 6u + 9 are perfect squares. We take their square roots and write: = −5u3 (u + 3)2 We must check that our middle term is correct. Because 2(u)(3) = 6u, we do have a perfect square trinomial and our result is correct. 29. In (21c + 16)(21c − 16), we have the exact same terms in the “First” and “Last” positions, with the ﬁrst set separated by a plus sign and the second set separated by a minus sign. Using the diﬀerence of squares pattern (a + b)(a − b) = a2 − b2 , we square the “First” and “Last” positions, then place a minus sign between the results. Hence: (21c + 16)(21c − 16) = (21c)2 − (16)2 = 441c2 − 256 Second Edition: 2012-2013 6.5. SPECIAL FORMS 401 31. In (5x + 19z)(5x − 19z), we have the exact same terms in the “First” and “Last” positions, with the ﬁrst set separated by a plus sign and the second set separated by a minus sign. Using the diﬀerence of squares pattern (a + b)(a − b) = a2 − b2 , we square the “First” and “Last” positions, then place a minus sign between the results. Hence: (5x + 19z)(5x − 19z) = (5x)2 − (19z)2 = 25x2 − 361z 2 33. In (3y 4 + 23z 4 )(3y 4 − 23z 4 ), we have the exact same terms in the “First” and “Last” positions, with the ﬁrst set separated by a plus sign and the second set separated by a minus sign. Using the diﬀerence of squares pattern (a + b)(a − b) = a2 − b2 , we square the “First” and “Last” positions, then place a minus sign between the results. Hence: (3y 4 + 23z 4)(3y 4 − 23z 4) = (3y 4 )2 − (23z 4 )2 = 9y 8 − 529z 8 35. In (8r5 + 19s5 )(8r5 − 19s5 ), we have the exact same terms in the “First” and “Last” positions, with the ﬁrst set separated by a plus sign and the second set separated by a minus sign. Using the diﬀerence of squares pattern (a + b)(a − b) = a2 − b2 , we square the “First” and “Last” positions, then place a minus sign between the results. Hence: (8r5 + 19s5 )(8r5 − 19s5 ) = (8r5 )2 − (19s5 )2 = 64r10 − 361s10 37. In 361x2 − 529, note that we have two perfect squares separated by a minus sign. Note that (19x)2 = 361x2 and (23)2 = 529. Using the diﬀerence of squares pattern a2 − b2 = (a + b)(a − b), we take the square roots, separate one pair with a plus sign and one pair with a minus sign. Hence: 361x2 − 529 = (19x + 23)(19x − 23) 39. In 16v 2 − 169, note that we have two perfect squares separated by a minus sign. Note that (4v)2 = 16v 2 and (13)2 = 169. Using the diﬀerence of squares pattern a2 − b2 = (a + b)(a − b), we take the square roots, separate one pair with a plus sign and one pair with a minus sign. Hence: 16v 2 − 169 = (4v + 13)(4v − 13) Second Edition: 2012-2013 CHAPTER 6. FACTORING 402 41. In 169x2 − 576y 2, note that we have two perfect squares separated by a minus sign. Note that (13x)2 = 169x2 and (24y)2 = 576y 2. Using the diﬀerence of squares pattern a2 − b2 = (a + b)(a − b), we take the square roots, separate one pair with a plus sign and one pair with a minus sign. Hence: 169x2 − 576y 2 = (13x + 24y)(13x − 24y) 43. In 529r2 − 289s2, note that we have two perfect squares separated by a minus sign. Note that (23r)2 = 529r2 and (17s)2 = 289s2 . Using the diﬀerence of squares pattern a2 − b2 = (a + b)(a − b), we take the square roots, separate one pair with a plus sign and one pair with a minus sign. Hence: 529r2 − 289s2 = (23r + 17s)(23r − 17s) 45. In 49r6 − 256t6 , note that we have two perfect squares separated by a minus sign. Note that (7r3 )2 = 49r6 and (16t3 )2 = 256t6 . Using the diﬀerence of squares pattern a2 − b2 = (a + b)(a − b), we take the square roots, separate one pair with a plus sign and one pair with a minus sign. Hence: 49r6 − 256t6 = (7r3 + 16t3 )(7r3 − 16t3 ) 47. In 36u10 − 25w10 , note that we have two perfect squares separated by a minus sign. Note that (6u5 )2 = 36u10 and (5w5 )2 = 25w10 . Using the diﬀerence of squares pattern a2 − b2 = (a + b)(a − b), we take the square roots, separate one pair with a plus sign and one pair with a minus sign. Hence: 36u10 − 25w10 = (6u5 + 5w5 )(6u5 − 5w5 ) 49. In 72y 5 − 242y 3, the GCF of 72y 5 and 242y 3 is 2y 3 . Factor out 2y 3 . 72y 5 − 242y 3 = 2y 3 (36y 2 − 121) Note that we have two perfect squares separated by a minus sign. Note that (6y)2 = 36y 2 and (11)2 = 121. Using the diﬀerence of squares pattern a2 −b2 = (a + b)(a − b), we take the square roots, separate one pair with a plus sign and one pair with a minus sign. Hence: 2y 3 (36y 2 − 121) = 2y 3 (6y + 11)(6y − 11) Thus, 72y 5 − 242y 3 = 2y 3 (6y + 11)(6y − 11). Second Edition: 2012-2013 6.5. SPECIAL FORMS 403 51. In 1444a3b − 324ab3, the GCF of 1444a3b and 324ab3 is 4ab. Factor out 4ab. 1444a3b − 324ab3 = 4ab(361a2 − 81b2 ) Note that we have two perfect squares separated by a minus sign. Note that (19a)2 = 361a2 and (9b)2 = 81b2 . Using the diﬀerence of squares pattern a2 − b2 = (a + b)(a − b), we take the square roots, separate one pair with a plus sign and one pair with a minus sign. Hence: 4ab(361a2 − 81b2 ) = 4ab(19a + 9b)(19a − 9b) Thus, 1444a3b − 324ab3 = 4ab(19a + 9b)(19a − 9b). 53. In 576x3 z − 1156xz 3, the GCF of 576x3 z and 1156xz 3 is 4xz. Factor out 4xz. 576x3 z − 1156xz 3 = 4xz(144x2 − 289z 2) Note that we have two perfect squares separated by a minus sign. Note that (12x)2 = 144x2 and (17z)2 = 289z 2. Using the diﬀerence of squares pattern a2 − b2 = (a + b)(a − b), we take the square roots, separate one pair with a plus sign and one pair with a minus sign. Hence: 4xz(144x2 − 289z 2) = 4xz(12x + 17z)(12x − 17z) Thus, 576x3 z − 1156xz 3 = 4xz(12x + 17z)(12x − 17z). 55. In 576t4 − 4t2 , the GCF of 576t4 and 4t2 is 4t2 . Factor out 4t2 . 576t4 − 4t2 = 4t2 (144t2 − 1) Note that we have two perfect squares separated by a minus sign. Note that (12t)2 = 144t2 and (1)2 = 1. Using the diﬀerence of squares pattern a2 − b2 = (a + b)(a − b), we take the square roots, separate one pair with a plus sign and one pair with a minus sign. Hence: 4t2 (144t2 − 1) = 4t2 (12t + 1)(12t − 1) Thus, 576t4 − 4t2 = 4t2 (12t + 1)(12t − 1). 57. In 81x4 − 256, we have the diﬀerence of two squares: (9x2 )2 = 81x4 and (16)2 = 256. First, we take the square roots, 9x2 and 16, then separate one set with a plus sign and the other set with a minus sign. 81x4 − 256 = (9x2 + 16)(9x2 − 16) Second Edition: 2012-2013 CHAPTER 6. FACTORING 404 Note that 9x2 + 16 is the sum of two squares and does not factor further. However, 9x2 − 16 is the diﬀerence of two squares: (3x)2 = 9x2 and (4)2 = 16. Take the square roots, 3x and 4, then separate one set with a plus sign and the other set with a minus sign. = (9x2 + 16)(3x + 4)(3x − 4) Done. We cannot factor further. 59. In 81x4 − 16, we have the diﬀerence of two squares: (9x2 )2 = 81x4 and (4)2 = 16. First, we take the square roots, 9x2 and 4, then separate one set with a plus sign and the other set with a minus sign. 81x4 − 16 = (9x2 + 4)(9x2 − 4) Note that 9x2 + 4 is the sum of two squares and does not factor further. However, 9x2 − 4 is the diﬀerence of two squares: (3x)2 = 9x2 and (2)2 = 4. Take the square roots, 3x and 2, then separate one set with a plus sign and the other set with a minus sign. = (9x2 + 4)(3x + 2)(3x − 2) Done. We cannot factor further. 61. We factor by grouping. Factor an z 2 out of the ﬁrst two terms and a −9 out of the second two terms. z 3 + z 2 − 9z − 9 = z 2 (z + 1) − 9(z + 1) Now we can factor out a z + 1. = (z 2 − 9)(z + 1) We’re still not done because z 2 − 9 is the diﬀerence of two squares and can be factored as follows: = (z + 3)(z − 3)(z + 1) 63. We factor by grouping. Factor an x2 out of the ﬁrst two terms and a −y 2 out of the second two terms. x3 − 2x2 y − xy 2 + 2y 3 = x2 (x − 2y) − y 2 (x − 2y) Now we can factor out a x − 2y. = (x2 − y 2 )(x − 2y) We’re still not done because x2 − y 2 is the diﬀerence of two squares and can be factored as follows: = (x + y)(x − y)(x − 2y) Second Edition: 2012-2013 6.5. SPECIAL FORMS 405 65. We factor by grouping. Factor an r2 out of the ﬁrst two terms and a −25t2 out of the second two terms. r3 − 3r2 t − 25rt2 + 75t3 = r2 (r − 3t) − 25t2 (r − 3t) Now we can factor out a r − 3t. = (r2 − 25t2 )(r − 3t) We’re still not done because r2 − 25t2 is the diﬀerence of two squares and can be factored as follows: = (r + 5t)(r − 5t)(r − 3t) 67. We factor by grouping. Factor an x2 out of the ﬁrst two terms and a −16 out of the second two terms. 2x3 + x2 − 32x − 16 = x2 (2x + 1) − 16(2x + 1) Now we can factor out a 2x + 1. = (x2 − 16)(2x + 1) We’re still not done because x2 − 16 is the diﬀerence of two squares and can be factored as follows: = (x + 4)(x − 4)(2x + 1) 69. The equation is nonlinear, so start by making one side equal to zero. 2x3 + 7x2 = 72x + 252 Original equation. 2x3 + 7x2 − 72x = 252 3 2 2x + 7x − 72x − 252 = 0 Subtract 72x from both sides. Subtract 252 from both sides. We now have a four-term expression, so we’ll try factoring by grouping. Factor x2 out of the ﬁrst two terms, and −36 out of the second two terms. x2 (2x + 7) − 36(2x + 7) = 0 2 (x − 36)(2x + 7) = 0 Factor by grouping. Factor out 2x + 7. The ﬁrst factor has two perfect squares separated by a minus sign, the diﬀerence of squares pattern. Take the square roots of each term, making one factor plus and one factor minus. (x + 6)(x − 6)(2x + 7) = 0 Factor using diﬀerence of squares. Second Edition: 2012-2013 CHAPTER 6. FACTORING 406 The polynomial is now completely factored. Use the zero product property to set each factor equal to zero, then solve each of the resulting equations. x+6=0 or x−6=0 x = −6 or 2x + 7 = 0 x=− x=6 7 2 Hence, the solutions of 2x3 +7x2 = 72x+252 are x = −6, x = 6, and x = −7/2. 71. The equation is nonlinear, so start by making one side equal to zero. x3 + 5x2 = 64x + 320 3 2 x + 5x − 64x = 320 3 2 x + 5x − 64x − 320 = 0 Original equation. Subtract 64x from both sides. Subtract 320 from both sides. We now have a four-term expression, so we’ll try factoring by grouping. Factor x2 out of the ﬁrst two terms, and −64 out of the second two terms. x2 (x + 5) − 64(x + 5) = 0 2 (x − 64)(x + 5) = 0 Factor by grouping. Factor out x + 5. The ﬁrst factor has two perfect squares separated by a minus sign, the diﬀerence of squares pattern. Take the square roots of each term, making one factor plus and one factor minus. (x + 8)(x − 8)(x + 5) = 0 Factor using diﬀerence of squares. The polynomial is now completely factored. Use the zero product property to set each factor equal to zero, then solve each of the resulting equations. x+8=0 or x = −8 x−8=0 or x+5=0 x=8 x = −5 Hence, the solutions of x3 + 5x2 = 64x + 320 are x = −8, x = 8, and x = −5. 73. The equation is nonlinear. Start by making one side equal to zero. 144x2 + 121 = 264x 2 144x − 264x + 121 = 0 Original equation. Subtract 264x from both sides. Note that the ﬁrst and last terms of the trinomial are perfect squares. Hence, it make sense to try and factor as a perfect square trinomial, taking the square roots of the ﬁrst and last terms. (12x − 11)2 = 0 Second Edition: 2012-2013 Factor. 6.5. SPECIAL FORMS 407 Of course, be sure to check the middle term. Because −2(12x)(11) = −264x, the middle term is correct. We can now use the zero product property to set each factor equal to zero and solve the resulting equations. 12x − 11 = 0 11 x= 12 or 12x − 11 = 0 11 x= 12 Hence, the only solution of 144x2 + 121 = 264x is x = 11/12. We encourage readers to check this solution. 75. The equation is nonlinear, so start the solution by making one side equal to zero. 16x2 = 169 Original equation. 2 16x − 169 = 0 Subtract 169 from both sides. (4x + 13)(4x − 13) = 0 Factor using diﬀerence of squares. Use the zero product property to set each factor equal to zero, then solve each equation for x. 4x + 13 = 0 x=− or 13 4 4x − 13 = 0 13 x= 4 Hence, the solutions of 16x2 = 169 are x = −13/4 and x = 13/4. We encourage readers to check each of these solutions. 77. The equation is nonlinear, so start the solution by making one side equal to zero. 9x2 = 25 Original equation. 2 9x − 25 = 0 Subtract 25 from both sides. (3x + 5)(3x − 5) = 0 Factor using diﬀerence of squares. Use the zero product property to set each factor equal to zero, then solve each equation for x. 3x + 5 = 0 x=− or 5 3 3x − 5 = 0 5 x= 3 Hence, the solutions of 9x2 = 25 are x = −5/3 and x = 5/3. We encourage readers to check each of these solutions. Second Edition: 2012-2013 CHAPTER 6. FACTORING 408 79. The equation is nonlinear. Start by making one side equal to zero. 256x2 + 361 = −608x Original equation. 2 256x + 608x + 361 = 0 Add 608x to both sides. Note that the ﬁrst and last terms of the trinomial are perfect squares. Hence, it make sense to try and factor as a perfect square trinomial, taking the square roots of the ﬁrst and last terms. (16x + 19)2 = 0 Factor. Of course, be sure to check the middle term. Because 2(16x)(19) = 608x, the middle term is correct. We can now use the zero product property to set each factor equal to zero and solve the resulting equations. 16x + 19 = 0 x=− or 16x + 19 = 0 19 16 x=− 19 16 Hence, the only solution of 256x2 + 361 = −608x is x = −19/16. We encourage readers to check this solution. 81. Algebraic solution. The equation is nonlinear, so make one side zero. Subtract x from both sides. x3 = x x3 − x = 0 Factor out the GCF. x(x2 − 1) = 0 Use the diﬀerence of squares pattern a2 − b2 = (a + b)(a − b) to factor. x(x + 1)(x − 1) = 0 Use the zero product property to set all three factors equal to zero, then solve the resulting equations. x=0 or x+1=0 x = −1 or x−1=0 x=1 Hence, the solutions are x = 0, x = −1, and x = 1. Calculator solution. Load the left- and right-hand sides of the equation x3 = x into Y1 and Y2 in the Y= menu, then select 6:ZStandard from the ZOOM menu to produce the following graph. Second Edition: 2012-2013 6.5. SPECIAL FORMS 409 We need to adjust the WINDOW parameters to make the points of intersection more visible. It seems that the points of intersection occur near the origin, so after some experimentation, we decided on the following parameters which produced the accompanying image. Next, use the 5:intersect utility from the CALC menu to ﬁnd the three points of intersection. Report the results on your homework as follows. Second Edition: 2012-2013 CHAPTER 6. FACTORING 410 y = x3 y 2 x −1 −2 y=x 0 1 2 −2 Hence, the solutions of x3 = x are x = −1, x = 0, and x = 1. Note how these agree with the algebraic solution. 83. Algebraic solution. The equation is nonlinear, so make one side zero. Subtract x from both sides. 4x3 = x 4x3 − x = 0 Factor out the GCF. x(4x2 − 1) = 0 Use the diﬀerence of squares pattern a2 − b2 = (a + b)(a − b) to factor. x(2x + 1)(2x − 1) = 0 Use the zero product property to set all three factors equal to zero, then solve the resulting equations. x=0 or 2x + 1 = 0 1 x=− 2 or 2x − 1 = 0 1 x= 2 Hence, the solutions are x = 0, x = −1/2, and x = 1/2. Calculator solution. Load the left- and right-hand sides of the equation 4x3 = x into Y1 and Y2 in the Y= menu, then select 6:ZStandard from the ZOOM menu to produce the following graph. Second Edition: 2012-2013 6.5. SPECIAL FORMS 411 We need to adjust the WINDOW parameters to make visible the points of intersection. It seems that the points of intersection occur near the origin. After some experimentation, we decided on the following parameters which produced the accompanying image. Next, use the 5:intersect utility from the CALC menu to ﬁnd the three points of intersection. Report the results on your homework as follows. Second Edition: 2012-2013 CHAPTER 6. FACTORING 412 y 1 −1 −0.5 0 y = 4x3 0.5 y=x 1 x −1 Hence, the solutions of 4x3 = x are x = −0.5, x = 0, and x = 0.5. Note how these agree with the algebraic solution, particularly since −0.5 = −1/2 and 0.5 = 1/2. Second Edition: 2012-2013 Chapter 7 Rational Functions 7.1 Negative Exponents 1. Recall what it means to raise a number to a power of −1. −1 Thus: = a −1 b b a An exponent of −1 has nothing to do with the sign of the answer. Invert a positive number, you get a positive result. Invert a negative number, you get a negative result. = Thus, to raise a number to a power of −1, simply invert the number. −1 1 =7 7 3. Recall what it means to raise a number to a power of −1. −1 Thus: = a −1 b = b a An exponent of −1 has nothing to do with the sign of the answer. Invert a positive number, you get a positive result. Invert a negative number, you get a negative result. Thus, to raise a number to a power of −1, simply invert the number. −1 9 8 =− − 9 8 413 CHAPTER 7. RATIONAL FUNCTIONS 414 5. Recall what it means to raise a number to a power of −1. −1 Thus: 1 a An exponent of −1 has nothing to do with the sign of the answer. Invert a positive number, you get a positive result. Invert a negative number, you get a negative result. a−1 = = Thus, to raise a number to a power of −1, simply invert the number. (18)−1 = 1 18 7. Recall what it means to raise a number to a power of −1. −1 Thus: 1 a An exponent of −1 has nothing to do with the sign of the answer. Invert a positive number, you get a positive result. Invert a negative number, you get a negative result. a−1 = = Thus, to raise a number to a power of −1, simply invert the number. (16)−1 = 1 16 9. In this case, we are multiplying like bases, so we’ll use the following law of exponents: am an = am+n . That is, we’ll repeat the base, then add the exponents. a−9 · a3 = a−9+3 =a −6 Repeat base, add exponents. Simplify. 11. In this case, we are multiplying like bases, so we’ll use the following law of exponents: am an = am+n . That is, we’ll repeat the base, then add the exponents. b−9 · b8 = b−9+8 =b −1 Second Edition: 2012-2013 Repeat base, add exponents. Simplify. 7.1. NEGATIVE EXPONENTS 415 13. In this case, we are multiplying like bases, so we’ll use the following law of exponents: am an = am+n . That is, we’ll repeat the base, then add the exponents. 29 · 2−4 = 29+(−4) =2 5 Repeat base, add exponents. Simplify. 15. In this case, we are multiplying like bases, so we’ll use the following law of exponents: am an = am+n . That is, we’ll repeat the base, then add the exponents. 9−6 · 9−5 = 9−6+(−5) =9 −11 Repeat base, add exponents. Simplify. 17. In this case, we are dividing like bases, so we’ll use the following law of exponents: am = am−n an That is, we’ll repeat the base, then subtract the exponents. 26 = 26−(−8) 2−8 = 26+8 =2 14 Repeat base, subtract exponents. Add the oopposite. Simplify. 19. In this case, we are dividing like bases, so we’ll use the following law of exponents: am = am−n an That is, we’ll repeat the base, then subtract the exponents. z −1 = z −1−9 z9 = z −1+(−9) =z −10 Repeat base, subtract exponents. Add the opposite. Simplify. Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 416 21. In this case, we are dividing like bases, so we’ll use the following law of exponents: am = am−n an That is, we’ll repeat the base, then subtract the exponents. w−9 = w−9−7 w7 = w−9+(−7) =w −16 Repeat base, subtract exponents. Add the opposite. Simplify. 23. In this case, we are dividing like bases, so we’ll use the following law of exponents: am = am−n an That is, we’ll repeat the base, then subtract the exponents. 7−3 = 7−3−(−1) 7−1 = 7−3+1 =7 −2 Repeat base, subtract exponents. Add the oopposite. Simplify. 25. In this case, we are raising a power to a power, so we’ll use the following law of exponents: (am )n = amn That is, we’ll repeat the base, then multiply the exponents. −1 4 t = t−1(4) =t −4 Repeat base, multiply exponents. Simplify. 27. In this case, we are raising a power to a power, so we’ll use the following law of exponents: n (am ) = amn That is, we’ll repeat the base, then multiply the exponents. −6 7 6 = 6−6(7) =6 −42 Second Edition: 2012-2013 Repeat base, multiply exponents. Simplify. 7.1. NEGATIVE EXPONENTS 417 29. In this case, we are raising a power to a power, so we’ll use the following law of exponents: n (am ) = amn That is, we’ll repeat the base, then multiply the exponents. −9 −9 z = z −9(−9) Repeat base, multiply exponents. = z 81 Simplify. 31. In this case, we are raising a power to a power, so we’ll use the following law of exponents: (am )n = amn That is, we’ll repeat the base, then multiply the exponents. −2 3 3 = 3−2(3) Repeat base, multiply exponents. = 3−6 Simplify. −1 . They are equivalent because the 33. Note that 4−3 is equivalent to 43 laws of exponents instruct us to multiply the exponents when raising a power −1 to another power. To evaluate 43 , we ﬁrst cube, then invert the result. −1 Repeat base and multiply exponents. 4−3 = 43 = 64−1 1 = 64 Cube: 43 = 64. Invert. Mental approach. It is much easier to simplify this expression mentally. In the expression 4−3 , the 3 means cube and the minus sign in front of the 3 means “invert.” To do this problem in our head, start with 4 and cube to get 64, then invert to get 1/64. −1 . They are equivalent because the 35. Note that 2−4 is equivalent to 24 laws of exponents instruct us to multiply the exponents when raising a power −1 to another power. To evaluate 24 , we ﬁrst raise to the fourth power, then invert the result. −1 2−4 = 24 Repeat base and multiply exponents. = 16−1 1 = 16 Raise to the fourth power: 24 = 16. Invert. Mental approach. It is much easier to simplify this expression mentally. In the expression 2−4 , the 4 means raise to the fourth power and the minus sign in front of the 4 means “invert.” To do this problem in our head, start with 2 and raise to the fourth power to get 16, then invert to get 1/16. Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 418 37. Note: −5 1 2 is equivalent to −1 5 1 2 They are equivalent because the laws of exponents instruct us to multiply the exponents when raising a power to another power. To evaluate [(1/2)5 ]−1 , we ﬁrst raise to the ﬁfth power, then invert the result. −5 5 −1 1 1 = 2 2 −1 1 = 32 = 32 Repeat base and multiply exponents. Raise to the ﬁfth power: (1/2)5 = 1/32. Invert. Mental approach. It is much easier to simplify this expression mentally. In −5 the expression (1/2) , the 5 means raise to the ﬁfth power and the minus sign in front of the 5 means “invert.” To do this problem in our head, start with 1/2 and raise to the ﬁfth power to get 1/32, then invert to get 32. 39. Note: −5 1 − 2 is equivalent to 5 −1 1 − 2 They are equivalent because the laws of exponents instruct us to multiply the exponents when raising a power to another power. To evaluate [(−1/2)5 ]−1 , we ﬁrst raise to the ﬁfth power, then invert the result. −5 5 −1 1 1 = − − 2 2 −1 1 = − 32 = −32 Repeat base and multiply exponents. Raise to the ﬁfth power: (−1/2)5 = −1/32. Invert. Mental approach. It is much easier to simplify this expression mentally. In −5 the expression (−1/2) , the 5 means raise to the ﬁfth power and the minus sign in front of the 5 means “invert.” To do this problem in our head, start with −1/2 and raise to the ﬁfth power to get −1/32, then invert to get −32. Second Edition: 2012-2013 7.1. NEGATIVE EXPONENTS 419 41. All the operators involved are multiplication, so the commutative and associative properties of multiplication allow us to change the order and grouping. We’ll show this regrouping here, but this step can be done mentally. −6 −9 8 −8 4u v 5u v = [(4)(5)](u−6 u8 )(v −9 v −8 ) Multiply 4 and 5 to get 20, then repeat the bases and add the exponents. = 20u−6+8 v −9+(−8) = 20u2 v −17 In the solution above, we’ve probably shown way too much work. It’s far easier to perform all of these steps mentally, multiplying the 4 and the 5 to get 20, then repeating bases and adding exponents, as in: −6 −9 8 −8 5u v = 20u2 v −17 4u v 43. All the operators involved are multiplication, so the commutative and associative properties of multiplication allow us to change the order and grouping. We’ll show this regrouping here, but this step can be done mentally. −6 −5 −4x4 y −2 = [(6)(−4)](x−6 x4 )(y −5 y −2 ) 6x y Multiply 6 and −4 to get −24, then repeat the bases and add the exponents. = −24x−6+4 y −5+(−2) = −24x−2 y −7 In the solution above, we’ve probably shown way too much work. It’s far easier to perform all of these steps mentally, multiplying the 6 and the −4 to get −24, then repeating bases and adding exponents, as in: −6 −5 −4x4 y −2 = −24x−2 y −7 6x y 45. The simplest approach is to ﬁrst write the expression as a product. −6 x7 z9 −6 x7 z 9 · = · 4 x−9 z −2 4 x−9 z −2 Reduce −6/4 to lowest terms. Because we are dividing like bases, we repeat the bases and subtract the exponents. 3 = − x7−(−9) z 9−(−2) 2 3 = − x7+9 z 9+2 2 3 = − x16 z 11 2 Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 420 In the solution above, we’ve shown way too much work. It’s far easier to imagine writing the expression as a product, reducing −6/4, then repeating bases and subtracting exponents, as in: −6 x7 z 9 3 = − x16 z 11 4 x−9 z −2 2 47. The simplest approach is to ﬁrst write the expression as a product. −6 a9 c6 −6 a9 c6 · −5 · −7 = −5 −7 −4 a c −4 a c Reduce −6/(−4) to lowest terms. Because we are dividing like bases, we repeat the bases and subtract the exponents. 3 9−(−5) 6−(−7) a c 2 3 = a9+5 c6+7 2 3 = a14 c13 2 = In the solution above, we’ve shown way too much work. It’s far easier to imagine writing the expression as a product, reducing −6/(−4), then repeating bases and subtracting exponents, as in: −6 a9 c6 3 = a14 c13 −4 a−5 c−7 2 49. The law of exponents (ab)n = an bn says that when you raise a product to a power, you must raise each factor to that power. So we begin by raising each factor to the power −5. −5 4 −5 −2 4 −5 w = 2−5 v −2 2v w To raise 2 to the −5, ﬁrst raise 2 to the ﬁfth power, then invert: 2−5 = 1/32. Next, raising a power to a power requires that we repeat the base and multiply exponents. = 1/32 v −2(−5) w4(−5) = 32 v 10 w−20 In the solution above , we’ve shown way too much work. It’s far easier to raise each factor to the ﬁfth power mentally: 2−5 = 1/32, then multiply each exponent on the remaining factors by 5, as in −2 4 −5 = 1/32 v 10 w−20 2v w Second Edition: 2012-2013 7.1. NEGATIVE EXPONENTS 421 51. The law of exponents (ab)n = an bn says that when you raise a product to a power, you must raise each factor to that power. So we begin by raising each factor to the fourth power. 4 7 4 −1 7 4 y = 34 x−1 3x y Note that 34 = 81. Next, raising a power to a power requires that we repeat the base and multiply exponents. = 81 x−1(4) y 7(4) = 81 x−4 y 28 In the solution above , we’ve shown way too much work. It’s far easier to raise each factor to the fourth power mentally: 34 = 81, then multiply each exponent on the remaining factors by 4, as in −1 7 4 = 81 x−4 y 28 3x y 53. The law of exponents (ab)n = an bn says that when you raise a product to a power, you must raise each factor to that power. So we begin by raising each factor to the ﬁfth power. 5 −7 5 6 −7 5 = 25 x6 z 2x z Note that 25 = 32. Next, raising a power to a power requires that we repeat the base and multiply exponents. = 32 x6(5) z −7(5) = 32 x30 z −35 In the solution above , we’ve shown way too much work. It’s far easier to raise each factor to the ﬁfth power mentally: 25 = 32, then multiply each exponent on the remaining factors by 5, as in 6 −7 5 = 32 x30 z −35 2x z 55. The law of exponents (ab)n = an bn says that when you raise a product to a power, you must raise each factor to that power. So we begin by raising each factor to the power −4. −4 8 −4 −4 8 −4 = 2−4 a−4 c 2a c Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 422 To raise 2 to the −4, ﬁrst raise 2 to the fourth power, then invert: 2−4 = 1/16. Next, raising a power to a power requires that we repeat the base and multiply exponents. = 1/16 a−4(−4) c8(−4) = 16 a16 c−32 In the solution above , we’ve shown way too much work. It’s far easier to raise each factor to the fourth power mentally: 2−4 = 1/16, then multiply each exponent on the remaining factors by 4, as in −4 8 −4 = 1/16 a16 c−32 2a c 57. Multiply numerator and denominator by y 2 . x5 y −2 x5 y −2 y 2 = · 2 3 z z3 y x5 y 0 y2z 3 x5 = 2 3 y z = Multiply numerator and denominator by y 2 Simplify: y −2 y 2 = y 0 Simplify: y 0 = 1 59. Multiply numerator and denominator by s2 . r9 s−2 r9 s−2 s2 = · 2 3 t t3 s r 9 s0 s 2 t3 r9 = 2 3 s t = Multiply numerator and denominator by s2 Simplify: s−2 s2 = s0 Simplify: s0 = 1 61. Multiply numerator and denominator by y 8 . x3 x3 y8 = · y −8 z 5 y −8 z 5 y 8 x3 y 8 y0z 5 x3 y 8 = 5 z = Second Edition: 2012-2013 Multiply numerator and denominator by y 8 Simplify: y −8 y 8 = y 0 Simplify: y 0 = 1 7.1. NEGATIVE EXPONENTS 423 63. Multiply numerator and denominator by v 4 . u9 u9 v4 = · v −4 w7 v −4 w7 v 4 Multiply numerator and denominator by v 4 u9 v 4 v 0 w7 u9 v 4 = w7 Simplify: v −4 v 4 = v 0 = Simplify: v 0 = 1 65. Multiply 7 and −7 to get −49, then repeat the base and add the exponents. (7x−1 )(−7x−1 ) = −49x−2 The negative exponent means invert, so we can replace x−2 with 1/x2 , then multiply numerators and denominators. −49 1 · 2 1 x −49 = 2 x = 67. Multiply 8 and 7 to get 56, then repeat the base and add the exponents. (8a−8 )(7a−7 ) = 56a−15 The negative exponent means invert, so we can replace a−15 with 1/a15 , then multiply numerators and denominators. 56 1 · 1 a15 56 = 15 a = 69. Write the expression as a product. 4 x−9 4x−9 = · 3 3 8x 8 x Reduce 4/8 to lowest terms, then repeat the base and subtract the exponents. = 1 −12 ·x 2 The negative exponent means invert, so we can replace x−12 with 1/x12 , then multiply numerators and denominators. 1 1 · 2 x12 1 = 12 2x = Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 424 71. Write the expression as a product. 6c2 6 c2 · = −4c7 −4 c7 Reduce 6/(−4) to lowest terms, then repeat the base and subtract the exponents. 3 = − · c−5 2 The negative exponent means invert, so we can replace c−5 with 1/c5 , then multiply numerators and denominators. 3 1 =− · 5 2 c 3 =− 5 2c 73. First raise each factor to the −4 power. (−3s9 )−4 = (−3)−4 (s9 )−4 Now, raise −3 to the fourth power, then invert to get 1/81. Next, because we are raising a power to a power, repeat the base and multiply the exponents. = 1 −36 s 81 The negative exponent means invert, so we can replace s−36 with 1/s36 , then multiply numerators and denominators. 1 1 · 81 s36 1 = 81s36 = 75. First raise each factor to the −5 power. (2y 4 )−5 = 2−5 (y 4 )−5 Now, raise 2 to the ﬁfth power, then invert to get 1/32. Next, because we are raising a power to a power, repeat the base and multiply the exponents. = Second Edition: 2012-2013 1 −20 y 32 7.2. SCIENTIFIC NOTATION 425 The negative exponent means invert, so we can replace y −20 with 1/y 20 , then multiply numerators and denominators. 1 1 · 32 y 20 1 = 32y 20 = 7.2 Scientific Notation 1. When the power of ten is a negative integer, it dictates the total number of decimal places to use in expressing the number in decimal form. In the case of 10−4 , the exponent −4 tells us to use 4 decimal places. This requires that we write a decimal point, 3 zeros, then the number 1. 10−4 = 0.0001 3. When the power of ten is a negative integer, it dictates the total number of decimal places to use in expressing the number in decimal form. In the case of 10−8 , the exponent −8 tells us to use 8 decimal places. This requires that we write a decimal point, 7 zeros, then the number 1. 10−8 = 0.00000001 5. When the power of ten is a whole number, it dictates the number of zeros that you should add after the number 1. In the case of 108 , the exponent 8 tells us to write 8 zeros after the number 1. 108 = 100000000 Next, we delimit our answer with commas in the appropriate places. 108 = 100, 000, 000 7. When the power of ten is a whole number, it dictates the number of zeros that you should add after the number 1. In the case of 107 , the exponent 7 tells us to write 7 zeros after the number 1. 107 = 10000000 Next, we delimit our answer with commas in the appropriate places. 107 = 10, 000, 000 Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 426 9. When multiplying by a power of ten, such as 10n , the exponent tells us how many places to move the decimal point. If n is greater than or equal to zero (nonegative), then we move the decimal point n places to the right. If n is less than zero (negative), then we move the decimal point n places to the left. In the case of 6506399.9 × 10−4, the exponent is negative, so we move the decimal point 4 places to the left. Hence: 6506399.9 × 10−4 = 650.63999 11. When multiplying by a power of ten, such as 10n , the exponent tells us how many places to move the decimal point. If n is greater than or equal to zero (nonegative), then we move the decimal point n places to the right. If n is less than zero (negative), then we move the decimal point n places to the left. In the case of 3959.430928 × 102 , the exponent is nonnegative, so we move the decimal point 2 places to the right. Hence: 3959.430928 × 102 = 395943.0928 13. When multiplying by a power of ten, such as 10n , the exponent tells us how many places to move the decimal point. If n is greater than or equal to zero (nonegative), then we move the decimal point n places to the right. If n is less than zero (negative), then we move the decimal point n places to the left. In the case of 440906.28 × 10−4 , the exponent is negative, so we move the decimal point 4 places to the left. Hence: 440906.28 × 10−4 = 44.090628 15. When multiplying by a power of ten, such as 10n , the exponent tells us how many places to move the decimal point. If n is greater than or equal to zero (nonegative), then we move the decimal point n places to the right. If n is less than zero (negative), then we move the decimal point n places to the left. In the case of 849.855115 × 104 , the exponent is nonnegative, so we move the decimal point 4 places to the right. Hence: 849.855115 × 104 = 8498551.15 17. Converting a number into scientifc notation requires that we convert the given number into the form a × 10k , where k is an integer and 1 ≤ |a| < 10. The requirement 1 ≤ |a| < 10 says that the magnitude of the number a must be greater than or equal to 1, but strictly less than 10. This means that there must be a single nonzero digit to the left of the decimal point. In the case of the number 390000, we must move the decimal point in the number 390000 ﬁve Second Edition: 2012-2013 7.2. SCIENTIFIC NOTATION 427 places to the left, then compensate by multiplying by multiplying by a power of ten so that the result is still identical to the original number. That is: 390000 = 3.9 × 105 Check: To check the solution, recall that multiplying by 105 moves the decimal point ﬁve places to the right. Hence: 3.9 × 105 = 390000 Thus, the solution checks. 19. Converting a number into scientifc notation requires that we convert the given number into the form a × 10k , where k is an integer and 1 ≤ |a| < 10. The requirement 1 ≤ |a| < 10 says that the magnitude of the number a must be greater than or equal to 1, but strictly less than 10. This means that there must be a single nonzero digit to the left of the decimal point. In the case of the number 0.202, we must move the decimal point in the number 0.202 one place to the right, then compensate by multiplying by multiplying by a power of ten so that the result is still identical to the original number. That is: 0.202 = 2.02 × 10−1 Check: To check the solution, recall that multiplying by 10−1 moves the decimal point one place to the left. Hence: 2.02 × 10−1 = 0.202 Thus, the solution checks. 21. Converting a number into scientifc notation requires that we convert the given number into the form a × 10k , where k is an integer and 1 ≤ |a| < 10. The requirement 1 ≤ |a| < 10 says that the magnitude of the number a must be greater than or equal to 1, but strictly less than 10. This means that there must be a single nonzero digit to the left of the decimal point. In the case of the number 0.81, we must move the decimal point in the number 0.81 one place to the right, then compensate by multiplying by multiplying by a power of ten so that the result is still identical to the original number. That is: 0.81 = 8.1 × 10−1 Check: To check the solution, recall that multiplying by 10−1 moves the decimal point one place to the left. Hence: 8.1 × 10−1 = 0.81 Thus, the solution checks. Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 428 23. Converting a number into scientifc notation requires that we convert the given number into the form a × 10k , where k is an integer and 1 ≤ |a| < 10. The requirement 1 ≤ |a| < 10 says that the magnitude of the number a must be greater than or equal to 1, but strictly less than 10. This means that there must be a single nonzero digit to the left of the decimal point. In the case of the number 0.0007264, we must move the decimal point in the number 0.0007264 four places to the right, then compensate by multiplying by multiplying by a power of ten so that the result is still identical to the original number. That is: 0.0007264 = 7.264 × 10−4 Check: To check the solution, recall that multiplying by 10−4 moves the decimal point four places to the left. Hence: 7.264 × 10−4 = 0.0007264 Thus, the solution checks. 25. Converting a number into scientifc notation requires that we convert the given number into the form a × 10k , where k is an integer and 1 ≤ |a| < 10. The requirement 1 ≤ |a| < 10 says that the magnitude of the number a must be greater than or equal to 1, but strictly less than 10. This means that there must be a single nonzero digit to the left of the decimal point. In the case of the number 0.04264 × 10−4 , we’ll ﬁrst convert the number 0.04264 into scientiﬁc notation, ignoring 10−4 for a moment. To do that, we must move the decimal point in the number 0.04264 two places to the right, then compensate by multiplying by multiplying by a power of ten so that the result is still identical to the original number. That is: 0.04264 × 10−4 = 4.264 × 10−2 × 10−4 To convert to a single power of 10, repeat the base and add the exponents. = 4.264 × 10−2+(−4) = 4.264 × 10−6 Thus, 0.04264 × 10−4 = 4.264 × 10−6 . 27. Converting a number into scientifc notation requires that we convert the given number into the form a × 10k , where k is an integer and 1 ≤ |a| < 10. The requirement 1 ≤ |a| < 10 says that the magnitude of the number a must be greater than or equal to 1, but strictly less than 10. This means that there must be a single nonzero digit to the left of the decimal point. In the case of the number 130000 × 103 , we’ll ﬁrst convert the number 130000 into Second Edition: 2012-2013 7.2. SCIENTIFIC NOTATION 429 scientiﬁc notation, ignoring 103 for a moment. To do that, we must move the decimal point in the number 130000 ﬁve places to the left, then compensate by multiplying by multiplying by a power of ten so that the result is still identical to the original number. That is: 130000 × 103 = 1.3 × 105 × 103 To convert to a single power of 10, repeat the base and add the exponents. = 1.3 × 105+3 = 1.3 × 108 Thus, 130000 × 103 = 1.3 × 108 . 29. Converting a number into scientifc notation requires that we convert the given number into the form a × 10k , where k is an integer and 1 ≤ |a| < 10. The requirement 1 ≤ |a| < 10 says that the magnitude of the number a must be greater than or equal to 1, but strictly less than 10. This means that there must be a single nonzero digit to the left of the decimal point. In the case of the number 30.04×105, we’ll ﬁrst convert the number 30.04 into scientiﬁc notation, ignoring 105 for a moment. To do that, we must move the decimal point in the number 30.04 one place to the left, then compensate by multiplying by multiplying by a power of ten so that the result is still identical to the original number. That is: 30.04 × 105 = 3.004 × 101 × 105 To convert to a single power of 10, repeat the base and add the exponents. = 3.004 × 101+5 = 3.004 × 106 Thus, 30.04 × 105 = 3.004 × 106 . 31. Converting a number into scientifc notation requires that we convert the given number into the form a × 10k , where k is an integer and 1 ≤ |a| < 10. The requirement 1 ≤ |a| < 10 says that the magnitude of the number a must be greater than or equal to 1, but strictly less than 10. This means that there must be a single nonzero digit to the left of the decimal point. In the case of the number 0.011×101, we’ll ﬁrst convert the number 0.011 into scientiﬁc notation, ignoring 101 for a moment. To do that, we must move the decimal point in the number 0.011 two places to the right, then compensate by multiplying by multiplying by a power of ten so that the result is still identical to the original number. That is: 0.011 × 101 = 1.1 × 10−2 × 101 Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 430 To convert to a single power of 10, repeat the base and add the exponents. = 1.1 × 10−2+1 = 1.1 × 10−1 Thus, 0.011 × 101 = 1.1 × 10−1 . 33. The notation 1.134E -1 is the calculator’s way of expressing scientiﬁc notation. That is, the notation 1.134E -1 is equivalent to the symbolism 1.134×10−1. Because the power of ten is negative, we move the decimal point 1 place to the left. Thus: 1.134E -1 = 1.134 × 10−1 = 0.1134 35. The notation 1.556E -2 is the calculator’s way of expressing scientiﬁc notation. That is, the notation 1.556E -2 is equivalent to the symbolism 1.556×10−2. Because the power of ten is negative, we move the decimal point 2 places to the left. Thus: 1.556E -2 = 1.556 × 10−2 = 0.01556 37. The notation 1.748E -4 is the calculator’s way of expressing scientiﬁc notation. That is, the notation 1.748E -4 is equivalent to the symbolism 1.748×10−4. Because the power of ten is negative, we move the decimal point 4 places to the left. Thus: 1.748E -4 = 1.748 × 10−4 = 0.0001748 39. We’ll use the approximations 2.5 ≈ 3 and 1.6 ≈ 2, which enable us to write: (2.5 × 10−1 )(1.6 × 10−7 ) ≈ (3 × 10−1 )(2 × 10−7 ) ≈ 6 × 10−1+(−7) ≈ 6 × 10−8 Next, enter (2.5 × 10−1 )(1.6 × 10−7 ) as 2.5E-1*1.6E-7 on your calculator, yielding the result shown in the following window. Second Edition: 2012-2013 7.2. SCIENTIFIC NOTATION 431 Hence, (2.5 × 10−1 )(1.6 × 10−7 ) = 4 × 10−8 . 41. We’ll use the approximations 1.4 ≈ 1 and 1.8 ≈ 2, which enable us to write: (1.4 × 107 )(1.8 × 10−4 ) ≈ (1 × 107 )(2 × 10−4 ) ≈ 2 × 107+(−4) ≈ 2 × 103 Next, enter (1.4×107)(1.8×10−4 ) as 1.4E7*1.8E-4 on your calculator, yielding the result shown in the following window. Hence, (1.4 × 107 )(1.8 × 10−4 ) = 2.52 × 103 . 43. We’ll use the approximations 3.2 ≈ 3 and 2.5 ≈ 3, which enables us to write: 3 × 10−5 3.2 × 10−5 ≈ 2.5 × 10−7 3 × 10−7 3 10−5 ≈ · −7 3 10 ≈ 1 · 10−5−(−7) ≈ 1 × 102 Push the MODE button, then highlight SCI mode and press ENTER. Move your cursor to the same row containing the FLOAT command, then highlight the number 2 and press ENTER. Press 2ND MODE to quit the MODE menu. Next, enter (3.2 × 10−5 )/(2.5 × 10−7 ) as 3.2E-5/2.5E-7 on your calculator, yielding the result shown in the following window. Second Edition: 2012-2013 432 CHAPTER 7. RATIONAL FUNCTIONS Hence, (3.2 × 10−5 )/(2.5 × 10−7 ) ≈ 1.28 × 102 . Don’t forget to return your calculator to its original mode by selecting NORMAL and FLOAT in the MODE menu. 45. We’ll use the approximations 5.9 ≈ 6 and 2.3 ≈ 2, which enables us to write: 5.9 × 103 6 × 103 ≈ 2.3 × 105 2 × 105 6 103 ≈ · 5 2 10 ≈ 3 · 103−5 ≈ 3 × 10−2 Push the MODE button, then highlight SCI mode and press ENTER. Move your cursor to the same row containing the FLOAT command, then highlight the number 2 and press ENTER. Press 2ND MODE to quit the MODE menu. Next, enter (5.9 × 103)/(2.3 × 105) as 5.9E3/2.3E5 on your calculator, yielding the result shown in the following window. Hence, (5.9 × 103 )/(2.3 × 105 ) ≈ 2.57 × 10−2 . Don’t forget to return your calculator to its original mode by selecting NORMAL and FLOAT in the MODE menu. 47. We need to form the ratio of biomass to the mass of the Earth 6.8 1013 6.8 × 1013 kg = · 5.9736 × 1024 kg 5.9736 1024 ≈ 1.14 × 10−11 Taking our number out of scientiﬁc notation we get 0.0000000000114. Changing this to a percent by moving the decimal two places to the right we get that the ratio of biomass to the mass of the Earth is about 0.00000000114%. Not a very large portion of the mass of our planet. Kind of makes you feel a bit insigniﬁcant. Second Edition: 2012-2013 7.3. SIMPLIFYING RATIONAL EXPRESSIONS 433 49. We are given the distance and the rate. What we want is the time traveled in days and years. To ﬁnd this we will use the model D = rt. Let’s solve this for t and we get t = D/r. Our distance is given to be D = 1.43 × 106 miles and our rate is r = 65 mph. Putting these values into our formula yields: 1.43 × 106 miles 65 miles per hour = 0.022 × 106 hours = 2, 200 hours t= We are asked to give our result in days and years. days 24 hours days = 2, 200 hours × 24 hours ≈ 916.7 days years = 916.7 days × 365 days × years = 916.7 days 365 days ≈ 2.5 years 2, 200 hours = 2, 200 hours × So, you would have to drive nonstop for about 916.7 days or about 2.5 years to cover all the paved roads in the USA. Be sure and bring a lot of coﬀee. 7.3 Simplifying Rational Expressions 1. Multiply numerators and denominators. 12s5 12 s5 = · 2 s 9 9s2 Now, there several diﬀerent ways you can reduce this answer to lowest terms, two of which are shown below. You can factor numerator and denominator, then cancel common factors. Or you can write the answer as a product, repeat the base and subtract exponents. 2·2·3·s·s·s·s·s 12s5 = 2 9s 3·3·s·s 2·2· 3 · s · s · s · s · s = 3 · 3 · s · s 4s3 = 3 12 s5 12s5 · = 2 9s 9 s2 4 = · s3 3 4s3 = 3 Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 434 3. Multiply numerators and denominators. 12 v 4 12v 4 = · 3 v 10 10v 3 Now, there several diﬀerent ways you can reduce this answer to lowest terms, two of which are shown below. You can factor numerator and denominator, then cancel common factors. Or you can write the answer as a product, repeat the base and subtract exponents. 2·2·3·v·v·v·v 12v 4 = 10v 3 2·5·v·v·v 2 · 2 · 3 · v · v · v · v = 2 · 5 · v · v · v 6v = 5 12 v 4 12v 4 · = 3 10v 10 v 3 6 = · v1 5 6v = 5 5. Invert, then multiply. s5 9s2 s 5 t2 ÷ = · t4 t2 t4 9s2 5 2 s t = 2 4 9s t Now, there several diﬀerent ways you can reduce this answer to lowest terms, two of which are shown below. You can factor numerator and denominator, then cancel common factors. Or you can write the answer as a product, repeat the base and subtract exponents. s·s·s·s·s·t·t s 5 t2 = 9s2 t4 3·3·s·s·t·t·t·t s · s · s · s · s · t · t = 3 · 3 · s · s · t · t · t · t s3 = 2 9t 1 s 5 t2 s 5 t2 = · · 9s2 t4 9 s 2 t4 1 = · s3 · t−2 9 s3 = 2 9t 7. Invert, then multiply. b4 9b2 b 4 c2 ÷ 2 = 4· 2 4 c c c 9b b 4 c2 = 2 4 9b c Now, there several diﬀerent ways you can reduce this answer to lowest terms, two of which are shown below. Second Edition: 2012-2013 7.3. SIMPLIFYING RATIONAL EXPRESSIONS 435 You can factor numerator and denominator, then cancel common factors. Or you can write the answer as a product, repeat the base and subtract exponents. b 4 c2 b·b·b·b·c·c = 9b2 c4 3·3·b·b·c·c·c·c b · b · b · b · c · c = 3 · 3 · b · b · c · c · c · c b2 = 2 9c b 4 c2 1 b 4 c2 · = · 9b2 c4 9 b 2 c4 1 = · b2 · c−2 9 b2 = 2 9c 9. Becase we have a common denominator, we can simply add the numerators, placing the answer over the common denominator. − −10s + 19s 10s 19s + = 18 18 18 9s 18 s = 2 = Add the numerators over the common denominator. Simplify: −10s + 19s = 9s Reduce. 11. Becase we have a common denominator, we can simply subtract the numerators, placing the answer over the common denominator. 5 17 5 − 17 − = 9c 9c 9c −12 9c 4 =− 3c = Subtract the numerators over the common denominator. Subtract: 5 − 17 = −12 Reduce. 13. Becase we have a common denominator, we can simply subtract the numerators, placing the answer over the common denominator. − 8x 16x −8x − 16x − = 15yz 15yz 15yz −24 15yz 8x =− 5yz = Subtract the numerators over the common denominator. Subtract: −8x − 16x = −24x Reduce. Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 436 15. The smallest number divisible by both 10 and 2 is 10; i.e., LCD(10, 2) = 10. We must ﬁrst make equivalent fractions with a common denominator of 10. 9z 5z 9z + = 10 2 10 9z = 10 1 5z 5 + · 1 2 5 25z + 10 · Make equivalent fractions with LCD = 10. We can now add the numerators and put the result over the common denominator. 34z 10 17z = 5 = Add: 9z + 25z = 34z Reduce. 17. The smallest expression divisible by both 10v and 5v is 10v; i.e., LCD(10v, 5v) = 10v. We must ﬁrst make equivalent fractions with a common denominator of 10v. 4 3 3 − = 10v 5v 10v 3 = 10v 1 4 2 − · 1 5v 2 8 − 10v · Make equivalent fractions with LCD = 10v. We can now subtract the numerators and put the result over the common denominator. −5 10v 1 =− 2v = Subtract: 3 − 8 = −5 Reduce. 19. The smallest expression divisible by both 5st and 10st is 10st; i.e., LCD(5st, 10st) = 10st. We must ﬁrst make equivalent fractions with a common denominator of 10st. − 9r 8r 2 9r 1 8r − =− · − · 5st 10st 5st 2 10st 1 9r 16r − =− 10st 10st Make equivalent fractions with LCD = 10st. We can now subtract the numerators and put the result over the common denominator. −25r 10st 5r =− 2st = Second Edition: 2012-2013 Subtract: −16r − 9r = −25r Reduce. 7.3. SIMPLIFYING RATIONAL EXPRESSIONS 437 21. Prime factor each denominator, placing the results in exponential form. 18rs2 = 21 · 32 · r1 · s2 24r2 s = 23 · 31 · r2 · s1 To ﬁnd the LCD, list each factor that appears to the highest power that it appears. LCD = 23 · 32 · r2 · s2 Simplify. LCD = 8 · 9 · r2 · s2 LCD = 72r2 s2 After making equivalent fractions, place the sum of the numerators over this common denominator. 11 11 5 3s 5 4r = + · + · 18rs2 24r2 s 18rs2 4r 24r2 s 3s 44r 15s = + 72r2 s2 72r2 s2 44r + 15s = 72r2 s2 23. Prime factor each denominator, placing the results in exponential form. 24rs2 = 23 · 31 · r1 · s2 36r2 s = 22 · 32 · r2 · s1 To ﬁnd the LCD, list each factor that appears to the highest power that it appears. LCD = 23 · 32 · r2 · s2 Simplify. LCD = 8 · 9 · r2 · s2 LCD = 72r2 s2 After making equivalent fractions, place the sum of the numerators over this common denominator. 5 5 17 2s 17 3r = + · + · 24rs2 36r2 s 24rs2 3r 36r2 s 2s 15r 34s = + 72r2 s2 72r2 s2 15r + 34s = 72r2 s2 Second Edition: 2012-2013 438 CHAPTER 7. RATIONAL FUNCTIONS 25. Prime factor each denominator, placing the results in exponential form. 36y 3 = 22 · 32 · y 3 48z 3 = 24 · 31 · z 3 To ﬁnd the LCD, list each factor that appears to the highest power that it appears. LCD = 24 · 32 · y 3 · z 3 Simplify. LCD = 16 · 9 · y 3 · z 3 LCD = 144y 3 z 3 After making equivalent fractions, place the sum of the numerators over this common denominator. 7 11 7 4z 3 11 3y 3 + = · + · 36y 3 48z 3 36y 3 4z 3 48z 3 3y 3 28z 3 33y 3 = + 144y 3z 3 144y 3 z 3 3 3 28z + 33y = 144y 3 z 3 27. Prime factor each denominator, placing the results in exponential form. 48v 3 = 24 · 31 · v 3 36w3 = 22 · 32 · w3 To ﬁnd the LCD, list each factor that appears to the highest power that it appears. LCD = 24 · 32 · v 3 · w3 Simplify. LCD = 16 · 9 · v 3 · w3 LCD = 144v 3 w3 After making equivalent fractions, place the sum of the numerators over this common denominator. 5 13 5 3w3 13 4v 3 + = · + · 48v 3 36w3 48v 3 3w3 36w3 4v 3 3 15w 52v 3 = + 3 3 144v w 144v 3 w3 3 3 15w + 52v = 144v 3 w3 Second Edition: 2012-2013 7.3. SIMPLIFYING RATIONAL EXPRESSIONS 439 29. Prime factor each denominator, placing the results in exponential form. 50xy = 21 · 52 · x1 · y 1 40yz = 23 · 51 · y 1 · z 1 To ﬁnd the LCD, list each factor that appears to the highest power that it appears. LCD = 23 · 52 · x1 · y 1 · z 1 Simplify. LCD = 8 · 25 · x · y · z LCD = 200xyz After making equivalent fractions, place the sum of the numerators over this common denominator. 11 9 11 4z 9 5x − = · − · 50xy 40yz 50xy 4z 40yz 5x 45x 44z − = 200xyz 200xyz 44z − 45x = 200xyz 31. Prime factor each denominator, placing the results in exponential form. 50ab = 21 · 52 · a1 · b1 40bc = 23 · 51 · b1 · c1 To ﬁnd the LCD, list each factor that appears to the highest power that it appears. LCD = 23 · 52 · a1 · b1 · c1 Simplify. LCD = 8 · 25 · a · b · c LCD = 200abc After making equivalent fractions, place the sum of the numerators over this common denominator. 19 17 19 4c 17 5a − = · − · 50ab 40bc 50ab 4c 40bc 5a 76c 85a = − 200abc 200abc 76c − 85a = 200abc Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 440 33. We use the distributive property, dividing each term by 3. 6v + 12 6v 12 = + 3 3 3 = 2v + 4 Distribute 3. Simplify: 6v/3 = 2v and 12/3 = 4 35. We use the distributive property, dividing each term by 5. 25u + 45 25u 45 = + 5 5 5 = 5u + 9 Distribute 5. Simplify: 25u/5 = 5u and 45/5 = 9 37. We use the distributive property, dividing each term by s. 2s − 4 2s 4 = − s s s 4 =2− s Distribute s. Simplify: 2s/s = 2 39. We use the distributive property, dividing each term by r. 3r − 5 3r 5 = − r r r 5 =3− r Distribute r. Simplify: 3r/r = 3 41. We use the distributive property, dividing each term by x2 . 3x2 − 8x − 9 3x2 8x 9 = − 2 − 2 x2 x2 x x 9 8 =3− − 2 x x Distribute x2 . Simplify: 3x2 /x2 = 3 and 8x/x2 = 8/x 43. We use the distributive property, dividing each term by x2 . 2x2 − 3x − 6 2x2 3x 6 = − 2 − 2 x2 x2 x x 6 3 =2− − 2 x x Second Edition: 2012-2013 Distribute x2 . Simplify: 2x2 /x2 = 2 and 3x/x2 = 3/x 7.4. SOLVING RATIONAL EQUATIONS 441 45. We use the distributive property, dividing each term by 12t2 . 12t2 + 2t − 16 12t2 2t 16 = + − 12t2 12t2 12t2 12t2 1 4 =1+ − 6t 3t2 Distribute 12t2 . Simplify: 12t2 /(12t2 ) = 1, 2t/(12t2 ) = 1/(6t), and 16/(12t2) = 4/(3t2 ) 47. We use the distributive property, dividing each term by 4s2 . 4s2 + 2s − 10 4s2 2s 10 = + 2− 2 2 2 4s 4s 4s 4s 5 1 − =1+ 2s 2s2 Distribute 4s2 . Simplify: 4s2 /(4s2 ) = 1, 2s/(4s2 ) = 1/(2s), and 10/(4s2 ) = 5/(2s2 ) 7.4 Solving Rational Equations 1. The least common denominator (LCD) is x, so ﬁrst clear fractions by multiplying both sides of the equation by the LCD. 26 x = 11 + x 26 x[x] = 11 + x x 26 x[x] = x [11] + x x x2 = 11x + 26 Original equation. Multiply both sides by x. Distribute x. Cancel and simplify. The resulting equation is nonlinear (x is raised to a power larger than 1). Make one side zero. x2 − 11x = 26 2 x − 11x − 26 = 0 Subtract 11x from both sides. Subtract 26 from both sides. Compare x2 − 11x − 26 with ax2 + bx + c and note that ac = (1)(−26) and b = −11. The integer pair 2 and −13 have product ac = −26 and sum b = −11. Hence, the trinomial factors as follows. (x + 2)(x − 13) = 0 Use ac-method to factor. Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 442 Use the zero product property to complete the solution. Either the ﬁrst factor is zero or the second factor is zero. x+2 = 0 or x − 13 = 0 x = −2 x = 13 Hence, the solutions are x = −2 and x = 13. 3. The least common denominator (LCD) is x2 , so ﬁrst clear fractions by multiplying both sides of the equation by the LCD. 27 12 =− 2 1− Original equation. x x 12 27 Multiply both sides by x2 . x2 1 − = − 2 x2 x x 12 27 Distribute x2 . x2 [1] − x2 = − 2 x2 x x x2 − 12x = −27 Cancel and simplify. The resulting equation is nonlinear (x is raised to a power larger than 1). Make one side zero, then factor. x2 − 12x + 27 = 0 Add 27 to both sides. Compare x2 − 12x + 27 with ax2 + bx + c and note that ac = (1)(27) and b = −12. The integer pair −3 and −9 have product ac = 27 and sum b = −12. Hence, the trinomial factors as follows. (x − 3)(x − 9) = 0 Use ac-method to factor. Use the zero product property to complete the solution. Either the ﬁrst factor is zero or the second factor is zero. x−3=0 or x=3 x−9=0 x=9 Hence, the solutions are x = 3 and x = 9. 5. The least common denominator (LCD) is x2 , so ﬁrst clear fractions by multiplying both sides of the equation by the LCD. 11 10 = 2 1− Original equation. x x 11 10 Multiply both sides by x2 . x2 1 − = 2 x2 x x 10 11 Distribute x2 . x2 [1] − x2 = 2 x2 x x x2 − 10x = 11 Second Edition: 2012-2013 Cancel and simplify. 7.4. SOLVING RATIONAL EQUATIONS 443 The resulting equation is nonlinear (x is raised to a power larger than 1). Make one side zero, then factor. x2 − 10x − 11 = 0 Subtract 11 from both sides. Compare x2 − 10x − 11 with ax2 + bx + c and note that ac = (1)(−11) and b = −10. The integer pair −11 and 1 have product ac = −11 and sum b = −10. Hence, the trinomial factors as follows. (x − 11)(x + 1) = 0 Use ac-method to factor. Use the zero product property to complete the solution. Either the ﬁrst factor is zero or the second factor is zero. x − 11 = 0 x = 11 or x+1=0 x = −1 Hence, the solutions are x = 11 and x = −1. 7. The least common denominator (LCD) is x, so ﬁrst clear fractions by multiplying both sides of the equation by the LCD. 44 x=7+ x 44 x[x] = 7 + x x 44 x[x] = x [7] + x x x2 = 7x + 44 Original equation. Multiply both sides by x. Distribute x. Cancel and simplify. The resulting equation is nonlinear (x is raised to a power larger than 1). Make one side zero. x2 − 7x = 44 Subtract 7x from both sides. 2 x − 7x − 44 = 0 Subtract 44 from both sides. Compare x2 − 7x − 44 with ax2 + bx + c and note that ac = (1)(−44) and b = −7. The integer pair 4 and −11 have product ac = −44 and sum b = −7. Hence, the trinomial factors as follows. (x + 4)(x − 11) = 0 Use ac-method to factor. Use the zero product property to complete the solution. Either the ﬁrst factor is zero or the second factor is zero. x+4=0 or x − 11 = 0 x = −4 x = 11 Hence, the solutions are x = −4 and x = 11. Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 444 9. The least common denominator (LCD) is x2 , so ﬁrst clear fractions by multiplying both sides of the equation by the LCD. 8 12x = 97 − x 8 x [12x] = 97 − x x 8 x [12x] = x [97] − x x 12x2 = 97x − 8 Original equation. Multiply both sides by x. Distribute x. Cancel and simplify. The resulting equation is nonlinear (x is raised to a power larger than 1). Make one side zero 12x2 − 97x = −8 Subtract 97x from both sides. 2 12x − 97x + 8 = 0 Add 8 to both sides. Compare 12x2 − 97x + 8 with ax2 + bx + c and note that ac = (12)(8) and b = −97. The integer pair −1 and −96 have product ac = 96 and sum b = −97. Replace the middle term with a combination of like terms using this pair, then factor by grouping. 12x2 − x − 96x + 8 = 0 x(12x − 1) − 8(12x − 1) = 0 −97x = −x − 96x Factor by grouping. (x − 8)(12x − 1) = 0 Factor out 12x − 1. Use the zero product property to complete the solution. Either the ﬁrst factor is zero or the second factor is zero. x−8=0 or x=8 12x − 1 = 0 1 x= 12 Hence, the solutions are x = 8 and x = 1/12. 11. The least common denominator (LCD) is x2 , so ﬁrst clear fractions by multiplying both sides of the equation by the LCD. 3 19 =− 2 x x 19 3 x2 20 + = − 2 x2 x x 19 3 x2 [20] + x2 = − 2 x2 x x 20 + 20x2 + 19x = −3 Second Edition: 2012-2013 Original equation. Multiply both sides by x2 . Distribute x2 . Cancel and simplify. 7.4. SOLVING RATIONAL EQUATIONS 445 The resulting equation is nonlinear (x is raised to a power larger than 1). Make one side zero 20x2 + 19x + 3 = 0 Add 3 to both sides. Compare 20x2 + 19x + 3 with ax2 + bx + c and note that ac = (20)(3) and b = 19. The integer pair 4 and 15 have product ac = 60 and sum b = 19. Replace the middle term with a combination of like terms using this pair, then factor by grouping. 20x2 + 4x + 15x + 3 = 0 4x(5x + 1) + 3(5x + 1) = 0 19x = 4x + 15x Factor by grouping. (4x + 3)(5x + 1) = 0 Factor out 5x + 1. Use the zero product property to complete the solution. Either the ﬁrst factor is zero or the second factor is zero. 4x + 3 = 0 or 5x + 1 = 0 1 3 x=− 4 5 Hence, the solutions are x = −3/4 and x = −1/5. x=− 13. The least common denominator (LCD) is x2 , so ﬁrst clear fractions by multiplying both sides of the equation by the LCD. 11 Original equation. 8x = 19 − x 11 x [8x] = 19 − x Multiply both sides by x. x 11 Distribute x. x [8x] = x [19] − x x 8x2 = 19x − 11 Cancel and simplify. The resulting equation is nonlinear (x is raised to a power larger than 1). Make one side zero 8x2 − 19x = −11 2 8x − 19x + 11 = 0 Subtract 19x from both sides. Add 11 to both sides. Compare 8x2 − 19x + 11 with ax2 + bx + c and note that ac = (8)(11) and b = −19. The integer pair −8 and −11 have product ac = 88 and sum b = −19. Replace the middle term with a combination of like terms using this pair, then factor by grouping. 8x2 − 8x − 11x + 11 = 0 8x(x − 1) − 11(x − 1) = 0 (8x − 11)(x − 1) = 0 −19x = −8x − 11x Factor by grouping. Factor out x − 1. Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 446 Use the zero product property to complete the solution. Either the ﬁrst factor is zero or the second factor is zero. 8x − 11 = 0 11 x= 8 x−1=0 or x=1 Hence, the solutions are x = 11/8 and x = 1. 15. The least common denominator (LCD) is x2 , so ﬁrst clear fractions by multiplying both sides of the equation by the LCD. 1 6 = 2 x x 1 6 2 x 40 + = 2 x2 x x 6 1 x2 [40] + x2 = 2 x2 x x 40 + 40x2 + 6x = 1 Original equation. Multiply both sides by x2 . Distribute x2 . Cancel and simplify. The resulting equation is nonlinear (x is raised to a power larger than 1). Make one side zero 40x2 + 6x − 1 = 0 Subtract 1 from both sides. Compare 40x2 + 6x − 1 with ax2 + bx + c and note that ac = (40)(−1) and b = 6. The integer pair −4 and 10 have product ac = −40 and sum b = 6. Replace the middle term with a combination of like terms using this pair, then factor by grouping. 40x2 − 4x + 10x − 1 = 0 4x(10x − 1) + 1(10x − 1) = 0 6x = −4x + 10x Factor by grouping. (4x + 1)(10x − 1) = 0 Factor out 10x − 1. Use the zero product property to complete the solution. Either the ﬁrst factor is zero or the second factor is zero. 4x + 1 = 0 1 x=− 4 or 10x − 1 = 0 1 x= 10 Hence, the solutions are x = −1/4 and x = 1/10. Second Edition: 2012-2013 7.4. SOLVING RATIONAL EQUATIONS 447 17. The least common denominator (LCD) is x2 , so ﬁrst clear fractions by multiplying both sides of the equation by the LCD. 1 Original equation. 36x = −13 − x 1 x [36x] = −13 − x Multiply both sides by x. x 1 x [36x] = x [−13] − x Distribute x. x 36x2 = −13x − 1 Cancel and simplify. The resulting equation is nonlinear (x is raised to a power larger than 1). Make one side zero 36x2 + 13x = −1 2 36x + 13x + 1 = 0 Add 13x to both sides. Add 1 to both sides. Compare 36x2 + 13x + 1 with ax2 + bx + c and note that ac = (36)(1) and b = 13. The integer pair 9 and 4 have product ac = 36 and sum b = 13. Replace the middle term with a combination of like terms using this pair, then factor by grouping. 36x2 + 9x + 4x + 1 = 0 9x(4x + 1) + 1(4x + 1) = 0 (9x + 1)(4x + 1) = 0 13x = 9x + 4x Factor by grouping. Factor out 4x + 1. Use the zero product property to complete the solution. Either the ﬁrst factor is zero or the second factor is zero. 9x + 1 = 0 or 4x + 1 = 0 1 1 x=− x=− 9 4 Hence, the solutions are x = −1/9 and x = −1/4. Check: To check the solution x = −1/9, ﬁrst enter -1/9, push the STO button, then the X,T,θ,n button and the ENTER key. Next, enter the lefthand side of the equation as 36*X and press ENTER. Enter the right-hand side of the equation as -13 - 1/X and press ENTER. The results are the same (see the ﬁrst image on the left below). This veriﬁes that −1/9 is a solution of 36x = −13 − 1/x. The calculator screen on the right shows a similar check of the solution x = −1/4. Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 448 19. The least common denominator (LCD) is x2 , so ﬁrst clear fractions by multiplying both sides of the equation by the LCD. 1 14x = 9 − x 1 x [14x] = 9 − x x 1 x [14x] = x [9] − x x 14x2 = 9x − 1 Original equation. Multiply both sides by x. Distribute x. Cancel and simplify. The resulting equation is nonlinear (x is raised to a power larger than 1). Make one side zero 14x2 − 9x = −1 Subtract 9x from both sides. 2 14x − 9x + 1 = 0 Add 1 to both sides. Compare 14x2 − 9x + 1 with ax2 + bx + c and note that ac = (14)(1) and b = −9. The integer pair −2 and −7 have product ac = 14 and sum b = −9. Replace the middle term with a combination of like terms using this pair, then factor by grouping. 14x2 − 2x − 7x + 1 = 0 2x(7x − 1) − 1(7x − 1) = 0 −9x = −2x − 7x Factor by grouping. (2x − 1)(7x − 1) = 0 Factor out 7x − 1. Use the zero product property to complete the solution. Either the ﬁrst factor is zero or the second factor is zero. 2x − 1 = 0 1 x= 2 or 7x − 1 = 0 1 x= 7 Hence, the solutions are x = 1/2 and x = 1/7. Check: To check the solution x = 1/2, ﬁrst enter 1/2, push the STO button, then the X,T,θ,n button and the ENTER key. Next, enter the left-hand side of the equation as 14*X and press ENTER. Enter the right-hand side of the equation as 9 - 1/X and press ENTER. The results are the same (see the ﬁrst image on the left below). This veriﬁes that 1/2 is a solution of 14x = 9 − 1/x. The calculator screen on the right shows a similar check of the solution x = 1/7. Second Edition: 2012-2013 7.4. SOLVING RATIONAL EQUATIONS 449 21. The least common denominator (LCD) is x2 , so ﬁrst clear fractions by multiplying both sides of the equation by the LCD. 12 1 = 2 x x 1 12 2 x 1− = 2 x2 x x 1 12 x2 [1] − x2 = 2 x2 x x 1− Original equation. Multiply both sides by x2 . Distribute x2 . x2 − x = 12 Cancel and simplify. The resulting equation is nonlinear (x is raised to a power larger than 1). Make one side zero, then factor. x2 − x − 12 = 0 Subtract 12 from both sides. Compare x2 − x− 12 with ax2 + bx+ c and note that ac = (1)(−12) and b = −1. The integer pair 3 and −4 have product ac = −12 and sum b = −1. Hence, the trinomial factors as follows. (x + 3)(x − 4) = 0 Use ac-method to factor. Use the zero product property to complete the solution. Either the ﬁrst factor is zero or the second factor is zero. x+3=0 or x−4=0 x = −3 x=4 Hence, the solutions are x = −3 and x = 4. Graphical solution: Make one side of the equation zero. 1− 1 12 − 2 =0 x x Load the left-hand side of the equation into Y1 as 1-1/X-12/Xˆ2 (see image on the left), then select 6:ZStandard from the ZOOM menu to produce the image at the right. Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 450 Next, the solutions of 1− 1 12 =0 − x x2 are found by noting where the graph of y = 1 − 2/x − 12/x2 cross the xaxis. Select 2:zero from the CALC menu. Use the arrow keys to move the cursor to the left of the ﬁrst x-intercept, then press ENTER to set the “Left bound.” Next, move the cursor to the right of the ﬁrst x-intercept, then press ENTER to set the “Right bound.” Finally, leave the cursor where it is and press ENTER to set your “Guess.” The calculator responds with the result shown in the ﬁgure on the left. Repeat the zero-ﬁnding procedure to capture the coordinates of the second x-intercept (see the image on the right). Reporting the solution on your homework. y 10 y = 1 − 1/x − 12/x2 −10 −3 4 10 x −10 Note that the calculator solutions, −3 and 4, match the algebraic solutions. Second Edition: 2012-2013 7.4. SOLVING RATIONAL EQUATIONS 451 23. The least common denominator (LCD) is x2 , so ﬁrst clear fractions by multiplying both sides of the equation by the LCD. 44 2x = 3 + x 44 x [2x] = 3 + x x 44 x [2x] = x [3] + x x 2x2 = 3x + 44 Original equation. Multiply both sides by x. Distribute x. Cancel and simplify. The resulting equation is nonlinear (x is raised to a power larger than 1). Make one side zero 2x2 − 3x = 44 Subtract 3x from both sides. 2 2x − 3x − 44 = 0 Subtract 44 from both sides. Compare 2x2 − 3x − 44 with ax2 + bx + c and note that ac = (2)(−44) and b = −3. The integer pair −11 and 8 have product ac = −88 and sum b = −3. Replace the middle term with a combination of like terms using this pair, then factor by grouping. 2x2 − 11x + 8x − 44 = 0 x(2x − 11) + 4(2x − 11) = 0 −3x = −11x + 8x Factor by grouping. (x + 4)(2x − 11) = 0 Factor out 2x − 11. Use the zero product property to complete the solution. Either the ﬁrst factor is zero or the second factor is zero. x+4=0 or x = −4 2x − 11 = 0 11 x= 2 Hence, the solutions are x = −4 and x = 11/2. Graphical solution: Make one side of the equation zero. 2x − 3 − 44 =0 x Load the left-hand side of the equation into Y1 as 2*X-3-44/X (see image on the left), then select 6:ZStandard from the ZOOM menu to produce the image at the right. Second Edition: 2012-2013 452 CHAPTER 7. RATIONAL FUNCTIONS Next, the solutions of 2x − 3 − 44 =0 x are found by noting where the graph of y = 2x−3−44/x cross the x-axis. Select 2:zero from the CALC menu. Use the arrow keys to move the cursor to the left of the ﬁrst x-intercept, then press ENTER to set the “Left bound.” Next, move the cursor to the right of the ﬁrst x-intercept, then press ENTER to set the “Right bound.” Finally, leave the cursor where it is and press ENTER to set your “Guess.” The calculator responds with the result shown in the ﬁgure on the left. Repeat the zero-ﬁnding procedure to capture the coordinates of the second x-intercept (see the image on the right). Reporting the solution on your homework. Second Edition: 2012-2013 7.4. SOLVING RATIONAL EQUATIONS 453 y 10 y = 2x − 3 − 44/x −10 −4 10 5.5 x −10 Note that the calculator solutions, −4 and 5.5, match the algebraic solutions. 25. In the solution, we address each step of the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. Let x represent the unknown number. 2. Set up an equation. If the unknown number is x, then its reciprocal is 1/x. Thus, the “sum of a number and its reciprocal is 5/2” becomes: x+ 5 1 = x 2 3. Solve the equation. Clear the fractions by multiplying both sides by 2x, the least common denominator. 5 1 = x 2 1 5 2x x + = 2x x 2 5 1 = 2x 2x [x] + 2x x 2 x+ 2x2 + 2 = 5x Model equation. Multiply both sides by 2x. Distribute 2x. Cancel and simplify. The equation is nonlinear. Make one side zero. 2x2 − 5x + 2 = 0 Make one side zero. Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 454 The integer pair −1 and −4 has product ac = 4 and sum b = −5. Break up the middle term in the last equation into a sum of like terms using this pair, then factor by grouping. 2x2 − x − 4x + 2 = 0 −x − 4x = −5x. x(2x − 1) − 2(2x − 1) = 0 Factor by grouping. (x − 2)(2x − 1) = 0 Factor out 2x − 1. We can now use the zero product property to write: x−2=0 or x=2 2x − 1 = 0 1 x= 2 4. Answer the question. There are two possible numbers, 2 and 1/2. 5. Look back. The sum of the unknown number and its reciprocal is supposed to equal 5/2. The ﬁrst answer 2 has reciprocal 1/2. Their sum is: 2+ 2 1 1 1 =2· + · 2 2 2 1 4 1 = + 2 2 5 = 2 Thus, 2 is a valid solution. The second answer 1/2 has reciprocal 2, so it is clear that their sum is also 5/2. Hence, 1/2 is also a valid solution. 27. In the solution, we address each step of the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. Let x represent the unknown number. 2. Set up an equation. If the unknown number is x, then its reciprocal is 1/x. Thus, the “sum of a number and 8 times its reciprocal is 17/3” becomes: 1 17 x+8 = x 3 Or equivalently: x+ Second Edition: 2012-2013 8 17 = x 3 7.4. SOLVING RATIONAL EQUATIONS 455 3. Solve the equation. Clear the fractions by multiplying both sides by 3x, the least common denominator. 8 17 = x 3 8 17 3x x + = 3x x 3 17 8 = 3x 3x [x] + 3x x 3 x+ 3x2 + 24 = 17x Model equation. Multiply both sides by 3x. Distribute 3x. Cancel and simplify. The equation is nonlinear. Make one side zero. 3x2 − 17x + 24 = 0 Make one side zero. The integer pair −8 and −9 has product ac = 72 and sum b = −17. Break up the middle term in the last equation into a sum of like terms using this pair, then factor by grouping. 3x2 − 8x − 9x + 24 = 0 −8x − 9x = −17x. x(3x − 8) − 3(3x − 8) = 0 (x − 3)(3x − 8) = 0 Factor by grouping. Factor out 3x − 8. We can now use the zero product property to write: x−3=0 x=3 or 3x − 8 = 0 8 x= 3 4. Answer the question. There are two possible numbers, 3 and 8/3. 5. Look back. The sum of the unknown number and 8 times its reciprocal is supposed to equal 17/3. The ﬁrst answer 3 has reciprocal 1/3. Their sum of the ﬁrst number and 8 times its reciprocal is: 3+8· 3 1 1 1 =3· +8· · 3 3 3 1 9 8 = + 3 3 17 = 3 Thus, 3 is a valid solution. We’ll leave it to readers to check that the second solution is also valid. Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 456 7.5 Direct and Inverse Variation 1. Given the fact the s is proportional to t, we know immediately that s = kt, where k is the proportionality constant. Because we are given that s = 632 when t = 79, we can substitute 632 for s and 79 for t to determine k. s = kt s is proportional to t. 632 = k(79) 632 =k 79 k=8 Substitute 632 for s, 79 for t. Divide both sides by 79. Simplify. Substitute 8 for k in s = kt, then substitute 50 for t to determine s when t = 50. s = 8t s = 8(50) Substitue 8 for k. Substitute 50 for t. s = 400 Multiply: 8(50) = 400 Thus, s = 400 when t = 50. 3. Given the fact the s is proportional to the cube of t, we know immediately that s = kt3 , where k is the proportionality constant. Because we are given that s = 1588867 when t = 61, we can substitute 1588867 for s and 61 for t to determine k. s = kt3 s is proportional to the cube of t. 3 1588867 = k(61) Substitute 1588867 for s, 61 for t. 1588867 = k(226981) 1588867 =k 226981 k=7 Simplify: (61)3 = 226981 Divide both sides by 226981. Simplify. Substitute 7 for k in s = kt3 , then substitute 63 for t to determine s when t = 63. s = 7t3 Substitue 7 for k. 3 s = 7(63) Substitute 63 for t. s = 7(250047) Exponent ﬁrst: (63)3 = 250047 s = 1750329 Multiply: 7(250047) = 1750329. Thus, s = 1750329 when t = 63. Second Edition: 2012-2013 7.5. DIRECT AND INVERSE VARIATION 457 5. Given the fact the q is proportional to the square of c, we know immediately that q = kc2 , where k is the proportionality constant. Because we are given that q = 13448 when c = 82, we can substitute 13448 for q and 82 for c to determine k. q = kc2 q is proportional to the square of c. 2 13448 = k(82) Substitute 13448 for q, 82 for c. 13448 = k(6724) 13448 =k 6724 k=2 Simplify: (82)2 = 6724 Divide both sides by 6724. Simplify. Substitute 2 for k in q = kc2 , then substitute 29 for c to determine q when c = 29. q = 2c2 Substitue 2 for k. 2 q = 2(29) Substitute 29 for c. q = 2(841) q = 1682 Exponent ﬁrst: (29)2 = 841 Multiply: 2(841) = 1682. Thus, q = 1682 when c = 29. 7. Given the fact the y is proportional to the square of x, we know immediately that y = kx2 , where k is the proportionality constant. Because we are given that y = 14700 when x = 70, we can substitute 14700 for y and 70 for x to determine k. y = kx2 y is proportional to the square of x. 2 14700 = k(70) Substitute 14700 for y, 70 for x. 14700 = k(4900) 14700 =k 4900 k=3 Simplify: (70)2 = 4900 Divide both sides by 4900. Simplify. Substitute 3 for k in y = kx2 , then substitute 45 for x to determine y when x = 45. y = 3x2 Substitue 3 for k. 2 y = 3(45) Substitute 45 for x. y = 3(2025) Exponent ﬁrst: (45)2 = 2025 y = 6075 Multiply: 3(2025) = 6075. Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 458 Thus, y = 6075 when x = 45. 9. Given the fact the F is proportional to the cube of x, we know immediately that F = kx3 , where k is the proportionality constant. Because we are given that F = 214375 when x = 35, we can substitute 214375 for F and 35 for x to determine k. F = kx3 F is proportional to the cube of x. 3 214375 = k(35) Substitute 214375 for F , 35 for x. 214375 = k(42875) 214375 =k 42875 k=5 Simplify: (35)3 = 42875 Divide both sides by 42875. Simplify. Substitute 5 for k in F = kx3 , then substitute 36 for x to determine F when x = 36. F = 5x3 Substitue 5 for k. 3 F = 5(36) Substitute 36 for x. F = 5(46656) Exponent ﬁrst: (36)3 = 46656 F = 233280 Multiply: 5(46656) = 233280. Thus, F = 233280 when x = 36. 11. Given the fact the d is proportional to t, we know immediately that d = kt, where k is the proportionality constant. Because we are given that d = 496 when t = 62, we can substitute 496 for d and 62 for t to determine k. d = kt 496 = k(62) 496 =k 62 k=8 d is proportional to t. Substitute 496 for d, 62 for t. Divide both sides by 62. Simplify. Substitute 8 for k in d = kt, then substitute 60 for t to determine d when t = 60. d = 8t Substitue 8 for k. d = 8(60) Substitute 60 for t. d = 480 Multiply: 8(60) = 480 Thus, d = 480 when t = 60. Second Edition: 2012-2013 7.5. DIRECT AND INVERSE VARIATION 459 13. Given the fact the h is inversely proportional to x, we know immediately that k h= , x where k is the proportionality constant. Because we are given that h = 16 when x = 29, we can substitute 16 for h and 29 for x to determine k. k x k 16 = 29 k 29(16) = 29 29 h= h is inversely proportional to x. Substitute 16 for h, 29 for x. Multiply both sides by 29. 464 = k Cancel and simplify. Substitute 464 for k in h = k/x, then substitute 20 for x to determine h when x = 20. 464 x 464 h= 20 116 h= 5 Substitue 464 for k. h= Substitute 20 for x. Reduce. Thus, h = 116/5 when x = 20. 15. Given the fact the q is inversely proportional to the square of c, we know immediately that k q = 2, c where k is the proportionality constant. Because we are given that q = 11 when c = 9, we can substitute 11 for q and 9 for c to determine k. k c2 k 11 = (9)2 k 11 = 81 k 81(11) = 81 81 q= k = 891 q is inversely proportional to the square of c. Substitute 11 for q, 9 for c. Exponent ﬁrst: (9)2 = 81 Multiply both sides by 81. Cancel and simplify. Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 460 Substitute 891 for k in q = k/c2 , then substitute 3 for c to determine q when c = 3. 891 c2 891 q= (3)2 891 q= 9 q = 99 q= Substitue 891 for k. Substitute 3 for c. Exponent ﬁrst: (3)2 = 9 Reduce. Thus, q = 99 when c = 3. 17. Given the fact the F is inversely proportional to x, we know immediately that k F = , x where k is the proportionality constant. Because we are given that F = 19 when x = 22, we can substitute 19 for F and 22 for x to determine k. k x k 19 = 22 k 22(19) = 22 22 F = 418 = k F is inversely proportional to x. Substitute 19 for F , 22 for x. Multiply both sides by 22. Cancel and simplify. Substitute 418 for k in F = k/x, then substitute 16 for x to determine F when x = 16. 418 x 418 F = 16 209 F = 8 F = Substitue 418 for k. Substitute 16 for x. Reduce. Thus, F = 209/8 when x = 16. 19. Given the fact the y is inversely proportional to the square of x, we know immediately that k y = 2, x Second Edition: 2012-2013 7.5. DIRECT AND INVERSE VARIATION 461 where k is the proportionality constant. Because we are given that y = 14 when x = 4, we can substitute 14 for y and 4 for x to determine k. k x2 k 14 = (4)2 k 14 = 16 k 16(14) = 16 16 k = 224 y= y is inversely proportional to the square of x. Substitute 14 for y, 4 for x. Exponent ﬁrst: (4)2 = 16 Multiply both sides by 16. Cancel and simplify. Substitute 224 for k in y = k/x2 , then substitute 10 for x to determine y when x = 10. 224 x2 224 y= (10)2 224 y= 100 56 y= 25 y= Substitue 224 for k. Substitute 10 for x. Exponent ﬁrst: (10)2 = 100 Reduce. Thus, y = 56/25 when x = 10. 21. Given the fact the d is inversely proportional to the cube of t, we know immediately that k d = 3, t where k is the proportionality constant. Because we are given that d = 18 when t = 2, we can substitute 18 for d and 2 for t to determine k. k t3 k 18 = (2)3 k 18 = 8 k 8(18) = 8 8 d= k = 144 d is inversely proportional to the cube of t. Substitute 18 for d, 2 for t. Exponent ﬁrst: (2)3 = 8 Multiply both sides by 8. Cancel and simplify. Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 462 Substitute 144 for k in d = k/t3 , then substitute 3 for t to determine d when t = 3. 144 t3 144 d= (3)3 144 d= 27 16 d= 3 d= Substitue 144 for k. Substitute 3 for t. Exponent ﬁrst: (3)3 = 27 Reduce. Thus, d = 16/3 when t = 3. 23. Given the fact the q is inversely proportional to the cube of c, we know immediately that k q = 3, c where k is the proportionality constant. Because we are given that q = 16 when c = 5, we can substitute 16 for q and 5 for c to determine k. k c3 k 16 = (5)3 k 16 = 125 k 125(16) = 125 125 q= k = 2000 q is inversely proportional to the cube of c. Substitute 16 for q, 5 for c. Exponent ﬁrst: (5)3 = 125 Multiply both sides by 125. Cancel and simplify. Substitute 2000 for k in q = k/c3 , then substitute 6 for c to determine q when c = 6. 2000 c3 2000 q= (6)3 2000 q= 216 250 q= 27 q= Thus, q = 250/27 when c = 6. Second Edition: 2012-2013 Substitue 2000 for k. Substitute 6 for c. Exponent ﬁrst: (6)3 = 216 Reduce. 7.5. DIRECT AND INVERSE VARIATION 463 25. Let W represent the weight hung on the spring. Let x represent the distance the spring stretches. We’re told that the distance x the spring stretches is proportional to the amount of weight W hung on the spring. Hence, we can write: x = kW x is proportional to W . We’re told that a 2 pound weight stretches the spring 16 inches. Substitute 2 for W , 16 for x, then solve for k. 16 = k(2) 16 =k 2 k=8 Substitute 16 for x, 2 for W . Divide both sides by 2. Simplify. Substitute 8 for k in x = kW to produce: x = 8W Substitute 8 for k in x = kW . To determine the distance the spring will stretch when 5 pounds are hung on the spring, substitute 5 for W . x = 8(5) x = 40 Substitute 5 for W . Simplify. Thus, the spring will stretch 40 inches. 27. Given the fact that the intensity I of the light is inversely proportional to the square of the distance d from the light source, we know immediately that I= k , d2 where k is the proportionality constant. Because we are given that the intensity is I = 20 foot-candles at d = 4 feet from the light source, we can substitute 20 for I and 4 for d to determine k. k d2 k 20 = (4)2 k 20 = 16 320 = k I= I is inversely proportional to d2 . Substitute 20 for I, 4 for d. Exponent ﬁrst: (4)2 = 16 Multiply both sides by 25. Second Edition: 2012-2013 CHAPTER 7. RATIONAL FUNCTIONS 464 Substitute 320 for k in I = k/d2 , then substitute 18 for d to determine I when d = 18. 320 d2 320 I= (18)2 320 I= 324 I = 1.0 I= Substitue 320 for k. Substitute 18 for d. Simplify. Divide. Round to nearest tenth. Thus, the intensity of the light 18 feet from the light source is 1.0 foot-candles. 29. Let p represent the price per person and let N be the number of people who sign up for the camping experience. Because we are told that the price per person is inversely proportional to the number of people who sign up for the camping experience, we can write: p= k , N where k is the proportionality constant. Because we are given that the price per person is $204 when 18 people sign up, we can substitute 204 for p and 18 for N to determine k. k N k 204 = 18 3672 = k p= p is inversely proportional to N . Substitute 204 for p, 18 for N . Multiply both sides by 18. Substitute 3672 for k in p = k/N , then substitute 35 for N to determine p when N = 35. 3672 N 3672 p= 35 p = 105 p= Substitute 3672 for k. Substitute 35 for N . Round to the nearest dollar. Thus, the price per person is $105 if 35 people sign up for the camping experience. Second Edition: 2012-2013 Chapter 8 Quadratic Functions 8.1 Introduction to Radical Notation 1. We are looking for a number whose square is −400. • However, every time you square a real number, the result is never negative. Hence, −400 has no real square roots. 3. We are looking for a number whose square is −25. • However, every time you square a real number, the result is never negative. Hence, −25 has no real square roots. 5. We are looking for a number whose square is 49. • Because (−7)2 = 49, the negative square root of 49 is −7. • Because (7)2 = 49, the nonnegative square root of 49 is 7. Hence, 49 has two real square roots, −7 and 7. 7. We are looking for a number whose square is 324. • Because (−18)2 = 324, the negative square root of 324 is −18. • Because (18)2 = 324, the nonnegative square root of 324 is 18. Hence, 324 has two real square roots, −18 and 18. 465 CHAPTER 8. QUADRATIC FUNCTIONS 466 9. We are looking for a number whose square is −225. • However, every time you square a real number, the result is never negative. Hence, −225 has no real square roots. 11. Every time you square a real number, the result is never negative. Hence, the equation x2 = −225 has no real solutions. 13. There are two numbers whose square equals 361, namely −19 and 19. x2 = 361 x = ±19 Original equation. Two answers: (−19)2 = 361 and (19)2 = 361. Thus, the real solutions of x2 = 361 are x = −19 or x = 19. Writing x = ±19 (“x equals plus or minus 19) is a shortcut for writing x = −19 or x = 19. 15. Every time you square a real number, the result is never negative. Hence, the equation x2 = −400 has no real solutions. 17. There are two numbers whose square equals 169, namely −13 and 13. x2 = 169 x = ±13 Original equation. Two answers: (−13)2 = 169 and (13)2 = 169. Thus, the real solutions of x2 = 169 are x = −13 or x = 13. Writing x = ±13 (“x equals plus or minus 13) is a shortcut for writing x = −13 or x = 13. 19. There are two numbers whose square equals 625, namely −25 and 25. x2 = 625 x = ±25 Original equation. Two answers: (−25)2 = 625 and (25)2 = 625. Thus, the real solutions of x2 = 625 are x = −25 or x = 25. Writing x = ±25 (“x equals plus or minus 25) is a shortcut for writing x = −25 or x = 25. √ 21. The expression 64 calls for the nonnegative square root of 64. Because (8)2 = 64 and 8 is nonnegative, √ 64 = 8. Second Edition: 2012-2013 8.1. INTRODUCTION TO RADICAL NOTATION 467 √ 23. The expression − −256 calls for the negative square root of −256. √ Because you cannot square a real number and get −256, the expression − −256 is not a real number. √ 25. The expression − 361 calls for the negative square root of 361. Because (−19)2 = 361 and −19 is negative, √ − 361 = −19. √ 27. The expression − 100 calls for the negative square root of 100. Because (−10)2 = 100 and −10 is negative, √ − 100 = −10. √ 29. The expression 441 calls for the nonnegative square root of 441. Because (21)2 = 441 and 21 is nonnegative, √ 441 = 21. √ 31. If a > 0,√ then − a is the negative solution of x2 = a. Hence, when we substitute − a into the equation x2 = a, we must get a true statement: √ (− a)2 = a. Thus: √ (− 17)2 = 17. √ 33. If a > √ 0, then a is the nonnegative solution of x2 = a. Hence, when we substitute a into the equation x2 = a, we must get a true statement: √ ( a)2 = a. Thus: √ ( 59)2 = 59. √ 35. If a > 0,√ then − a is the negative solution of x2 = a. Hence, when we substitute − a into the equation x2 = a, we must get a true statement: √ (− a)2 = a. Thus: √ (− 29)2 = 29. Second Edition: 2012-2013 468 CHAPTER 8. QUADRATIC FUNCTIONS √ 37. If a > √ 0, then a is the nonnegative solution of x2 = a. Hence, when we substitute a into the equation x2 = a, we must get a true statement: √ ( a)2 = a. Thus: √ ( 79)2 = 79. 39. Enter each side of the equation x2 = 37 in the Y= menu, then adjust the WINDOW parameters so the intersection points are visible in the viewing window. Use the 5:intersect utility on the CALC menu to ﬁnd the points of intersection. Reporting the solution on your homework: Duplicate the image in your calculator’s viewing window on your homework page. Second Edition: 2012-2013 8.1. INTRODUCTION TO RADICAL NOTATION y 469 y = x2 50 y = 37 −10 −6.082763 10 x 6.082763 −50 Next, solve the equation algebraically, then enter the results in your calculator to see if they match those found above. x2 = 37 √ x = ± 37 Note how these solutions match those found using the 5:intersect utility on the calculator. 41. Enter each side of the equation x2 = 11 in the Y= menu, then adjust the WINDOW parameters so the intersection points are visible in the viewing window. Use the 5:intersect utility on the CALC menu to ﬁnd the points of intersection. Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 470 Reporting the solution on your homework: Duplicate the image in your calculator’s viewing window on your homework page. y y = x2 30 y = 11 −10 −3.316625 3.316625 10 x −30 Next, solve the equation algebraically, then enter the results in your calculator to see if they match those found above. x2 = 11 √ x = ± 11 Note how these solutions match those found using the 5:intersect utility on the calculator. Second Edition: 2012-2013 8.2. SIMPLIFYING RADICAL EXPRESSIONS 8.2 471 Simplifying Radical Expressions √ √ √ 1. Use the property a b = ab to multiply the radicals. √ √ 5 13 = (5)(13) √ = 65 √ √ √ 3. Use the property a b = ab to multiply the radicals. √ √ 17 2 = (17)(2) √ = 34 √ √ √ 5. Use the property a b = ab to multiply the radicals. √ √ 5 17 = (5)(17) √ = 85 7. From 9. From Check: Use the graphing calculator to check the result. Check: Use the graphing calculator to check the result. Check: Use the graphing calculator to check the result. √ √ 56, we can factor out a perfect square, in this case 4. √ √ √ 56 = 4 14 Factor out a perfect square. √ √ Simplify: 4 = 2. = 2 14 √ √ 99, we can factor out a perfect square, in this case 9. √ √ √ 99 = 9 11 Factor out a perfect square. √ √ Simplify: 9 = 3. = 3 11 Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 472 11. From 13. From 15. From 17. From 19. From 21. From 23. From √ √ 150, we can factor out a perfect square, in this case 25. √ √ √ 150 = 25 6 Factor out a perfect square. √ √ Simplify: 25 = 5. =5 6 √ √ 40, we can factor out a perfect square, in this case 4. √ √ √ 40 = 4 10 Factor out a perfect square. √ √ = 2 10 Simplify: 4 = 2. √ √ 28, we can factor out a perfect square, in this case 4. √ √ √ 28 = 4 7 Factor out a perfect square. √ √ Simplify: 4 = 2. =2 7 √ √ 153, we can factor out a perfect square, in this case 9. √ √ √ 153 = 9 17 Factor out a perfect square. √ √ = 3 17 Simplify: 9 = 3. √ √ 50, we can factor out a perfect square, in this case 25. √ √ √ 50 = 25 2 Factor out a perfect square. √ √ =5 2 Simplify: 25 = 5. √ √ 18, we can factor out a perfect square, in this case 9. √ √ √ 18 = 9 2 Factor out a perfect square. √ √ Simplify: 9 = 3. =3 2 √ √ 44, we can factor out a perfect square, in this case 4. √ √ √ 44 = 4 11 Factor out a perfect square. √ √ = 2 11 Simplify: 4 = 2. Second Edition: 2012-2013 8.2. SIMPLIFYING RADICAL EXPRESSIONS 25. From 473 √ √ 104, we can factor out a perfect square, in this case 4. √ √ √ 104 = 4 26 Factor out a perfect square. √ √ = 2 26 Simplify: 4 = 2. 27. First, write out the Pythagorean Theorem, then substitute the given values in the appropriate places. a2 + b 2 = c2 2 2 Pythagorean Theorem. 2 (14) + b = (16) 2 Substitute: 14 for a, 16 for c. Square: (14)2 = 196, (16)2 = 256. 196 + b = 256 b2 = 60 Subtract 196 from both sides. √ √ The equation b2 = 60 has two real solutions, b = − 60 and b = 60. However, in this situation, b represents the length of one leg of the right triangle and must be a positive number. Hence: b= √ 60 Nonnegative square root. However, this answer is√not in simple radical form. In this case, we can factor out the perfect square 4. √ √ 4 15 √ b = 2 15 b= √ √ √ 60 = 4 15. √ 4 = 2. √ Thus, the length of the missing leg is b = 2 15. 29. First, write out the Pythagorean Theorem, then substitute the given values in the appropriate places. a2 + b 2 = c2 2 2 Pythagorean Theorem. 2 (3) + b = (25) 2 9 + b = 625 b2 = 616 Substitute: 3 for a, 25 for c. Square: (3)2 = 9, (25)2 = 625. Subtract 9 from both sides. √ √ The equation b2 = 616 has two real solutions, b = − 616 and b = 616. However, in this situation, b represents the length of one leg of the right triangle and must be a positive number. Hence: b= √ 616 Nonnegative square root. Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 474 However, this answer is√not in simple radical form. In this case, we can factor out the perfect square 4. √ √ √ √ √ 616 = 4 154. b = 4 154 √ √ 4 = 2. b = 2 154 √ Thus, the length of the missing leg is b = 2 154. 31. First, write out the Pythagorean Theorem, then substitute the given values in the appropriate places. a2 + b 2 = c2 2 2 (2) + (12) = c 4 + 144 = c 2 2 148 = c2 Pythagorean Theorem. Substitute: 2 for a, 12 for b. Square: (2)2 = 4, (12)2 = 144. Add: 4 + 144 = 148. √ √ The equation c2 = 148 has two real solutions, c = − 148 and c = 148. However, in this situation, c represents the length of the hypotenuse and must be a positive number. Hence: √ Nonnegative square root. c = 148 However, this answer is√not in simple radical form. In this case, we can factor out the perfect square 4. √ √ √ √ √ c = 4 37 148 = 4 37. √ √ c = 2 37 4 = 2. √ Thus, the length of the hypotenuse is c = 2 37. 33. First, write out the Pythagorean Theorem, then substitute the given values in the appropriate places. a2 + b 2 = c2 2 2 (10) + (14) = c 100 + 196 = c 2 2 296 = c2 Pythagorean Theorem. Substitute: 10 for a, 14 for b. Square: (10)2 = 100, (14)2 = 196. Add: 100 + 196 = 296. √ √ The equation c2 = 296 has two real solutions, c = − 296 and c = 296. However, in this situation, c represents the length of the hypotenuse and must be a positive number. Hence: √ Nonnegative square root. c = 296 Second Edition: 2012-2013 8.2. SIMPLIFYING RADICAL EXPRESSIONS 475 However, this answer is√not in simple radical form. In this case, we can factor out the perfect square 4. √ √ √ √ √ 296 = 4 74. c = 4 74 √ √ 4 = 2. c = 2 74 √ Thus, the length of the hypotenuse is c = 2 74. 35. To ﬁnd the area of the shaded region, subtract the area of the triangle from the area of the semicircle. Area of shaded region = Area of semicircle − Area of triangle To ﬁnd the area of the semicircle, we’ll need to ﬁnd the radius of the circle. Note that the hypotenuse of the right triangle ABC is the diameter of the circle. We can use the Pythagorean Theorem to ﬁnd its length. (AB)2 = (AC)2 + (BC)2 (AB)2 = (4)2 + (3)2 (AB)2 = 16 + 9 (AB)2 = 25 Hence, the diameter of the semicircle is AB = 5. The radius of the semicircle is 1/2 of the diameter. Hence, the radius of the semicircle is r = 5/2. The area of a full circle is given by the formula A = πr2 , so the area of the semicircle is found by: 1 2 πr 2 2 5 1 = π 2 2 25 π = 8 To ﬁnd the area of ABC, we take half of the base times the height. Area of semicircle = 1 (3)(4) 2 =6 Area of triangle = We can now ﬁnd the area of the shaded region. Area of shaded region = Area of semicircle − Area of triangle 25 = π−6 8 Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 476 37. We follow the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. Let x represent the length of the shorter leg of the right triangle. Because the longer leg is 10 feet longer than twice the length of the shorter leg, its length is 2x + 10. The length of the hypotenuse is 4 feet longer than three times the length of its shorter leg, so its length is 3x + 4. A sketch will help us maintain focus. 3x + 4 x 2x + 10 2. Set up an equation. By the Pythagorean Theorem, the sum of the squares of the legs must equal the square of the hypotenuse. x2 + (2x + 10)2 = (3x + 4)2 3. Solve the equation. Use the shortcut (a + b)2 = a2 + 2ab + b2 to expand. x2 + (2x + 10)2 = (3x + 4)2 x2 + 4x2 + 40x + 100 = 9x2 + 24x + 16 Simplify the left-hand side. 5x2 + 40x + 100 = 9x2 + 24x + 16 The equation is nonlinear, so make one side zero by subtracting 5x2 , 40x, and 100 from both sides of the equation. 0 = 4x2 − 16x − 84 Note that each coeﬃcient is divisible by 4. Divide both sides of the equation by 4. 0 = x2 − 4x − 21 Note that the integer pair 3 and −7 has a product equal to ac = (1)(−21) = −21 and sum equal to b = −4. Because the leading coeﬃcient is a 1, we can “drop this pair in place” to factor. 0 = (x − 7)(x + 3) Hence, x = 7 and x = −3. Second Edition: 2012-2013 8.2. SIMPLIFYING RADICAL EXPRESSIONS 477 4. Answer the question. Because x represents the length of the shortest side of the right triangle, and length is a positive quantity, we discard the answer x = −3. Next, if the length of the shorter leg is x = 7 feet, then the length of the longer leg is 2x + 10 = 2(7) + 10, or 24 feet. Finally, the length of the hypotenuse is 3x + 4 = 3(7) + 4, or 25 feet. 5. Look back. Note that the length of the longer leg is 24 feet, which is 10 feet longer than twice 7 feet, the length of the shorter leg. The length of the hypotenuse is 25, which is 4 feet longer than three times 7 feet, the length of the shorter leg. But do the numbers satisfy the Pythagorean Theorem? 25 7 24 That is, is it true that ? 72 + 242 = 252 Simplify each square. ? 49 + 576 = 625 Note that this last statement is true, so our solution checks. 39. As always, we obey the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. We’ll create a well-marked diagram for this purpose, letting h represent the distance between the base of the garage wall and the upper tip of the ladder. Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 478 19 ft h 5 ft 2. Set up an equation. Using the Pythagorean Theorem, we can write: 52 + h2 = 192 Pythagorean Theorem. 2 Square: 52 = 25 and 192 = 361. 25 + h = 361 3. Solve the equation. h2 = 336 √ h = 336 Subtract 25 from both sides. h will be the nonnegative square root. 4. Answer the question. As we’re asked for a decimal approximation, we won’t worry about simple radical form in this situation. The ladder √ reaches 336 feet up the wall. Using a calculator, this is about 18.3 feet, rounded to the nearest tenth of a foot. 5. Look back. Understand that when we use 18.3 ft, an approximation, our solution will only check approximately. 19 ft 5 ft Second Edition: 2012-2013 18.3 ft 8.3. COMPLETING THE SQUARE 479 Using the Pythagorean Theorem: 52 + (18.3)2 = 192 25 + 334.89 = 361 359.89 = 361 The approximation is not perfect, but it seems close enough! 8.3 Completing the Square 1. There are two square roots of 84, one positive and one negative. x = 84 √ x = ± 84 Original equation. Two square roots of 84. However, these answers are not in simple radical form. In this case, we can √ factor out a perfect square, namely 4, then simplify. √ √ x = ± 4 21 √ x = ±2 21 √ √ √ 84 = 4 21 √ Simplify: 4 = 2 √ Therefore, the solutions of x2 = 84 are x = ±2 21. 3. There are two square roots of 68, one positive and one negative. x = 68 √ x = ± 68 Original equation. Two square roots of 68. However, these answers are not in simple radical form. In this case, we can √ factor out a perfect square, namely 4, then simplify. √ √ x = ± 4 17 √ x = ±2 17 √ √ √ 68 = 4 17 √ Simplify: 4 = 2 √ Therefore, the solutions of x2 = 68 are x = ±2 17. 5. Consider again the equation x2 = −16 You cannot square a real number and get a negative result. Hence, this equation has no real solutions. Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 480 7. There are two square roots of 124, one positive and one negative. x = 124 √ x = ± 124 Original equation. Two square roots of 124. However, these answers are not in simple radical form. In this case, we can √ factor out a perfect square, namely 4, then simplify. √ √ x = ± 4 31 √ x = ±2 31 √ √ √ 124 = 4 31 √ Simplify: 4 = 2 √ Therefore, the solutions of x2 = 124 are x = ±2 31. 9. Much like the solutions of x2 = 36 are x = ±6, we use a similar approach on (x + 19)2 = 36 to obtain: (x + 19)2 = 36 x + 19 = ±6 Original equation. There are two square roots. To complete the solution, subtract 19 to both sides of the equation. x = −19 ± 6 Subtract 19 from both sides. Note that this means that there are two answers, namely: x = −19 − 6 or x = −25 x = −19 + 6 x = −13 11. Much like the solutions of x2 = 100 are x = ±10, we use a similar approach on (x + 14)2 = 100 to obtain: (x + 14)2 = 100 x + 14 = ±10 Original equation. There are two square roots. To complete the solution, subtract 14 to both sides of the equation. x = −14 ± 10 Subtract 14 from both sides. Note that this means that there are two answers, namely: x = −14 − 10 x = −24 Second Edition: 2012-2013 or x = −14 + 10 x = −4 8.3. COMPLETING THE SQUARE 481 13. Using the shortcut (a + b)2 = a2 + 2ab + b2 , we square the binomial as follows: (x + 23)2 = x2 + 2(x)(23) + (23)2 = x2 + 46x + 529 15. Using the shortcut (a + b)2 = a2 + 2ab + b2 , we square the binomial as follows: (x + 11)2 = x2 + 2(x)(11) + (11)2 = x2 + 22x + 121 17. Using the shortcut (a − b)2 = a2 − 2ab + b2 , we square the binomial as follows: (x − 25)2 = x2 − 2(x)(25) + (25)2 = x2 − 50x + 625 19. Using the shortcut a2 + 2ab + b2 = (a + b)2 , we factor the trinomial by taking the square roots of the ﬁrst and last terms, then writing: x2 + 24x + 144 = (x + 12)2 Note that 2(x)(12) = 24x, so the middle term checks. 21. Using the shortcut a2 − 2ab + b2 = (a − b)2 , we factor the trinomial by taking the square roots of the ﬁrst and last terms, then writing: x2 − 34x + 289 = (x − 17)2 Note that 2(x)(17) = 34x, so the middle term checks. 23. Using the shortcut a2 − 2ab + b2 = (a − b)2 , we factor the trinomial by taking the square roots of the ﬁrst and last terms, then writing: x2 − 20x + 100 = (x − 10)2 Note that 2(x)(10) = 20x, so the middle term checks. Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 482 25. Compare x2 − 20x with x2 + bx and note that b = −20. 1. Take one-half of −20: −10 2. Square the result of step 1: (−10)2 = 100 3. Add the result of step 2 to x2 − 20x: x2 − 20x + 100 Check: Note that the ﬁrst and last terms of x2 −20x+100 are perfect squares. Take the square roots of the ﬁrst and last terms and factor as follows: x2 − 20x + 100 = (x − 10)2 Note that 2(x)(−10) = −20x, so the middle term checks. 27. Compare x2 − 6x with x2 + bx and note that b = −6. 1. Take one-half of −6: −3 2. Square the result of step 1: (−3)2 = 9 3. Add the result of step 2 to x2 − 6x: x2 − 6x + 9 Check: Note that the ﬁrst and last terms of x2 − 6x + 9 are perfect squares. Take the square roots of the ﬁrst and last terms and factor as follows: x2 − 6x + 9 = (x − 3)2 Note that 2(x)(−3) = −6x, so the middle term checks. 29. Compare x2 + 20x with x2 + bx and note that b = 20. 1. Take one-half of 20: 10 2. Square the result of step 1: (10)2 = 100 3. Add the result of step 2 to x2 + 20x: x2 + 20x + 100 Check: Note that the ﬁrst and last terms of x2 +20x+100 are perfect squares. Take the square roots of the ﬁrst and last terms and factor as follows: x2 + 20x + 100 = (x + 10)2 Note that 2(x)(10) = 20x, so the middle term checks. Second Edition: 2012-2013 8.3. COMPLETING THE SQUARE 483 31. Compare x2 + 7x with x2 + bx and note that b = 7. 1. Take one-half of 7: 7/2 2. Square the result of step 1: (7/2)2 = 49/4 3. Add the result of step 2 to x2 + 7x: x2 + 7x + 49/4 Check: Note that the ﬁrst and last terms of x2 +7x+49/4 are perfect squares. Take the square roots of the ﬁrst and last terms and factor as follows: 2 7 49 = x+ x2 + 7x + 4 2 Note that 2(x)(7/2) = 7x, so the middle term checks. 33. Compare x2 + 15x with x2 + bx and note that b = 15. 1. Take one-half of 15: 15/2 2. Square the result of step 1: (15/2)2 = 225/4 3. Add the result of step 2 to x2 + 15x: x2 + 15x + 225/4 Check: Note that the ﬁrst and last terms of x2 + 15x + 225/4 are perfect squares. Take the square roots of the ﬁrst and last terms and factor as follows: 2 15 225 2 = x+ x + 15x + 4 2 Note that 2(x)(15/2) = 15x, so the middle term checks. 35. Compare x2 − 5x with x2 + bx and note that b = −5. 1. Take one-half of −5: −5/2 2. Square the result of step 1: (−5/2)2 = 25/4 3. Add the result of step 2 to x2 − 5x: x2 − 5x + 25/4 Check: Note that the ﬁrst and last terms of x2 −5x+25/4 are perfect squares. Take the square roots of the ﬁrst and last terms and factor as follows: 2 5 25 = x− x2 − 5x + 4 2 Note that 2(x)(−5/2) = −5x, so the middle term checks. Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 484 37. Note that the equation x2 = 18x − 18 is nonlinear (there is a power of x greater than one). Normal procedure would be to ﬁrst make one side zero. x2 − 18x + 18 = 0 We would then calculate ac = (1)(18). However, after some exploration, we discover that there is no integer pair whose product is ac = 18 and whose sum is b = −18. Hence, this trinomial will not factor using the ac-method. Therefore, we’ll use the technique of completing the square to solve the equation. First, move the constant term to the right-hand side of the equation. x2 − 18x = −18 On the left, take one-half of the coeﬃcient of x: (1/2)(−18) = −9. Square the result: (−9)2 = 81. Add this result to both sides of the equation. x2 − 18x + 81 = −18 + 81 x2 − 18x + 81 = 63 We can now factor the left-hand side as a perfect square trinomial. (x − 9)2 = 63 Now, as in Examples ??, ??, and ??, we can take the square root of both sides of the equation. Remember, there are two square roots. √ x − 9 = ± 63 The right hand side√ is not in simple radical form. We can factor out a perfect square, in this case 9. √ √ x−9=± 9 7 √ x − 9 = ±3 7 Finally, add 9 to both sides of the equation. √ x=9±3 7 √ √ Thus, the equation x2 = 18x−18 has two answers, x = 9−3 7 and x = 9+3 7. 39. Note that the equation x2 = 16x − 16 is nonlinear (there is a power of x greater than one). Normal procedure would be to ﬁrst make one side zero. x2 − 16x + 16 = 0 Second Edition: 2012-2013 8.3. COMPLETING THE SQUARE 485 We would then calculate ac = (1)(16). However, after some exploration, we discover that there is no integer pair whose product is ac = 16 and whose sum is b = −16. Hence, this trinomial will not factor using the ac-method. Therefore, we’ll use the technique of completing the square to solve the equation. First, move the constant term to the right-hand side of the equation. x2 − 16x = −16 On the left, take one-half of the coeﬃcient of x: (1/2)(−16) = −8. Square the result: (−8)2 = 64. Add this result to both sides of the equation. x2 − 16x + 64 = −16 + 64 x2 − 16x + 64 = 48 We can now factor the left-hand side as a perfect square trinomial. (x − 8)2 = 48 Now, as in Examples ??, ??, and ??, we can take the square root of both sides of the equation. Remember, there are two square roots. √ x − 8 = ± 48 The right hand side√ is not in simple radical form. We can factor out a perfect square, in this case 16. √ √ x − 8 = ± 16 3 √ x − 8 = ±4 3 Finally, add 8 to both sides of the equation. √ x=8±4 3 √ √ Thus, the equation x2 = 16x−16 has two answers, x = 8−4 3 and x = 8+4 3. 41. Note that the equation x2 = −16x − 4 is nonlinear (there is a power of x greater than one). Normal procedure would be to ﬁrst make one side zero. x2 + 16x + 4 = 0 We would then calculate ac = (1)(4). However, after some exploration, we discover that there is no integer pair whose product is ac = 4 and whose sum is b = 16. Hence, this trinomial will not factor using the ac-method. Therefore, Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 486 we’ll use the technique of completing the square to solve the equation. First, move the constant term to the right-hand side of the equation. x2 + 16x = −4 On the left, take one-half of the coeﬃcient of x: (1/2)(16) = 8. Square the result: (8)2 = 64. Add this result to both sides of the equation. x2 + 16x + 64 = −4 + 64 x2 + 16x + 64 = 60 We can now factor the left-hand side as a perfect square trinomial. (x + 8)2 = 60 Now, as in Examples ??, ??, and ??, we can take the square root of both sides of the equation. Remember, there are two square roots. √ x + 8 = ± 60 The right hand side√ is not in simple radical form. We can factor out a perfect square, in this case 4. √ √ x + 8 = ± 4 15 √ x + 8 = ±2 15 Finally, subtract 8 from both sides of the equation. √ x = −8 ± 2 15 √ Thus, the equation x2 = −16x − 4 has two answers, x = −8 − 2 15 and √ x = −8 + 2 15. 43. Note that the equation x2 = 18x − 9 is nonlinear (there is a power of x greater than one). Normal procedure would be to ﬁrst make one side zero. x2 − 18x + 9 = 0 We would then calculate ac = (1)(9). However, after some exploration, we discover that there is no integer pair whose product is ac = 9 and whose sum is b = −18. Hence, this trinomial will not factor using the ac-method. Therefore, we’ll use the technique of completing the square to solve the equation. First, move the constant term to the right-hand side of the equation. x2 − 18x = −9 Second Edition: 2012-2013 8.3. COMPLETING THE SQUARE 487 On the left, take one-half of the coeﬃcient of x: (1/2)(−18) = −9. Square the result: (−9)2 = 81. Add this result to both sides of the equation. x2 − 18x + 81 = −9 + 81 x2 − 18x + 81 = 72 We can now factor the left-hand side as a perfect square trinomial. (x − 9)2 = 72 Now, as in Examples ??, ??, and ??, we can take the square root of both sides of the equation. Remember, there are two square roots. √ x − 9 = ± 72 The right hand side√ is not in simple radical form. We can factor out a perfect square, in this case 36. √ √ x − 9 = ± 36 2 √ x − 9 = ±6 2 Finally, add 9 to both sides of the equation. √ x=9±6 2 √ √ Thus, the equation x2 = 18x−9 has two answers, x = 9−6 2 and x = 9+6 2. 45. Note that the equation x2 = 16x − 8 is nonlinear (there is a power of x greater than one). Normal procedure would be to ﬁrst make one side zero. x2 − 16x + 8 = 0 We would then calculate ac = (1)(8). However, after some exploration, we discover that there is no integer pair whose product is ac = 8 and whose sum is b = −16. Hence, this trinomial will not factor using the ac-method. Therefore, we’ll use the technique of completing the square to solve the equation. First, move the constant term to the right-hand side of the equation. x2 − 16x = −8 On the left, take one-half of the coeﬃcient of x: (1/2)(−16) = −8. Square the result: (−8)2 = 64. Add this result to both sides of the equation. x2 − 16x + 64 = −8 + 64 x2 − 16x + 64 = 56 Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 488 We can now factor the left-hand side as a perfect square trinomial. (x − 8)2 = 56 Now, as in Examples ??, ??, and ??, we can take the square root of both sides of the equation. Remember, there are two square roots. √ x − 8 = ± 56 The right hand side√ is not in simple radical form. We can factor out a perfect square, in this case 4. √ √ x − 8 = ± 4 14 √ x − 8 = ±2 14 Finally, add 8 to both sides of the equation. √ x = 8 ± 2 14 √ Thus,√the equation x2 = 16x − 8 has two answers, x = 8 − 2 14 and x = 8 + 2 14. 47. Note that the equation x2 = −18x − 18 is nonlinear (there is a power of x greater than one). Normal procedure would be to ﬁrst make one side zero. x2 + 18x + 18 = 0 We would then calculate ac = (1)(18). However, after some exploration, we discover that there is no integer pair whose product is ac = 18 and whose sum is b = 18. Hence, this trinomial will not factor using the ac-method. Therefore, we’ll use the technique of completing the square to solve the equation. First, move the constant term to the right-hand side of the equation. x2 + 18x = −18 On the left, take one-half of the coeﬃcient of x: (1/2)(18) = 9. Square the result: (9)2 = 81. Add this result to both sides of the equation. x2 + 18x + 81 = −18 + 81 x2 + 18x + 81 = 63 We can now factor the left-hand side as a perfect square trinomial. (x + 9)2 = 63 Second Edition: 2012-2013 8.3. COMPLETING THE SQUARE 489 Now, as in Examples ??, ??, and ??, we can take the square root of both sides of the equation. Remember, there are two square roots. √ x + 9 = ± 63 The right hand side√ is not in simple radical form. We can factor out a perfect square, in this case 9. √ √ x+9=± 9 7 √ x + 9 = ±3 7 Finally, subtract 9 from both sides of the equation. √ x = −9 ± 3 7 √ Thus, the equation x2 = −18x − 18 has two answers, x = −9 − 3 7 and √ x = −9 + 3 7. 49. Note that the equation x2 = −16x − 20 is nonlinear (there is a power of x greater than one). Normal procedure would be to ﬁrst make one side zero. x2 + 16x + 20 = 0 We would then calculate ac = (1)(20). However, after some exploration, we discover that there is no integer pair whose product is ac = 20 and whose sum is b = 16. Hence, this trinomial will not factor using the ac-method. Therefore, we’ll use the technique of completing the square to solve the equation. First, move the constant term to the right-hand side of the equation. x2 + 16x = −20 On the left, take one-half of the coeﬃcient of x: (1/2)(16) = 8. Square the result: (8)2 = 64. Add this result to both sides of the equation. x2 + 16x + 64 = −20 + 64 x2 + 16x + 64 = 44 We can now factor the left-hand side as a perfect square trinomial. (x + 8)2 = 44 Now, as in Examples ??, ??, and ??, we can take the square root of both sides of the equation. Remember, there are two square roots. √ x + 8 = ± 44 Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 490 The right hand side√ is not in simple radical form. We can factor out a perfect square, in this case 4. √ √ x + 8 = ± 4 11 √ x + 8 = ±2 11 Finally, subtract 8 from both sides of the equation. √ x = −8 ± 2 11 √ Thus, the equation x2 = −16x − 20 has two answers, x = −8 − 2 11 and √ x = −8 + 2 11. 51. Note that the equation x2 = −18x − 1 is nonlinear (there is a power of x greater than one). Normal procedure would be to ﬁrst make one side zero. x2 + 18x + 1 = 0 We would then calculate ac = (1)(1). However, after some exploration, we discover that there is no integer pair whose product is ac = 1 and whose sum is b = 18. Hence, this trinomial will not factor using the ac-method. Therefore, we’ll use the technique of completing the square to solve the equation. First, move the constant term to the right-hand side of the equation. x2 + 18x = −1 On the left, take one-half of the coeﬃcient of x: (1/2)(18) = 9. Square the result: (9)2 = 81. Add this result to both sides of the equation. x2 + 18x + 81 = −1 + 81 x2 + 18x + 81 = 80 We can now factor the left-hand side as a perfect square trinomial. (x + 9)2 = 80 Now, as in Examples ??, ??, and ??, we can take the square root of both sides of the equation. Remember, there are two square roots. √ x + 9 = ± 80 The right hand side√ is not in simple radical form. We can factor out a perfect square, in this case 16. √ √ x + 9 = ± 16 5 √ x + 9 = ±4 5 Second Edition: 2012-2013 8.3. COMPLETING THE SQUARE 491 Finally, subtract 9 from both sides of the equation. √ x = −9 ± 4 5 √ Thus, the equation x2 = −18x − 1 has two answers, x = −9 − 4 5 and √ x = −9 + 4 5. 53. First, move the constant −17 to the right-hand side of of the equation. x2 − 2x − 17 = 0 2 x − 2x = 17 Original equation. Add 17 to both sides. Take half of the coeﬃcient of x: (1/2)(−2) = −1. Square, (−1)2 = 1, then add this result to both sides of the equation. x2 − 2x + 1 = 17 + 1 2 (x − 1) = 18 √ x − 1 = ± 18 √ √ x−1=± 9 2 √ x − 1 = ±3 2 √ x=1±3 2 Add 1 to both sides. Factor left-hand side. There are two square roots. Factor out a perfect square. √ Simplify: 9 = 3. Add 1 to both sides. Graphical solution: Enter the equation y = x2 − 2x − 17 in Y1 of the Y= menu (see the ﬁrst image below). After some experimentation, we settled on the WINDOW parameters shown in the middle image below. Once you’ve entered these WINDOW parameters, push the GRAPH button to produce the the graph of y = x2 − 2x − 17, as shown in the rightmost image below. We’re looking for solutions of x2 − 2x − 17 = 0, so we need to locate where the graph of y = x2 − 2x − 17 intercepts the x-axis. That is, we need to ﬁnd the zeros of y = x2 − 2x − 17. Select 2:zero from the CALC menu, move the cursor slightly to the left of the ﬁrst x-intercept and press ENTER in response to “Left bound.” Move the cursor slightly to the right of the ﬁrst x-intercept and press ENTER in response to “Right bound.” Leave the cursor where it sits Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 492 and press ENTER in response to “Guess.” The calculator responds by ﬁnding the x-coordinate of the x-intercept, as shown in the ﬁrst image below. Repeat the process to ﬁnd the second x-intercept of y = x2 − 2x − 17 shown in the second image below. Reporting the solution on your homework: Duplicate the image in your calculator’s viewing window on your homework page. Use a ruler to draw all lines, but freehand any curves. y 20 −3.242641 5.242641 −10 10 −20 x y = x2 − 2x − 17 Comparing exact and calculator approximations. How well do the √ graphing calculator √ solutions compare with the exact solutions, x = 1 − 3 2 and x = 1 + 3 2? After entering each in the calculator, the comparison is excellent! Second Edition: 2012-2013 8.3. COMPLETING THE SQUARE 493 55. First, move the constant −3 to the right-hand side of of the equation. x2 − 6x − 3 = 0 2 x − 6x = 3 Original equation. Add 3 to both sides. Take half of the coeﬃcient of x: (1/2)(−6) = −3. Square, (−3)2 = 9, then add this result to both sides of the equation. x2 − 6x + 9 = 3 + 9 2 (x − 3) = 12 √ x − 3 = ± 12 √ √ x−3=± 4 3 √ x − 3 = ±2 3 √ x=3±2 3 Add 9 to both sides. Factor left-hand side. There are two square roots. Factor out a perfect square. √ Simplify: 4 = 2. Add 3 to both sides. Graphical solution: Enter the equation y = x2 − 6x − 3 in Y1 of the Y= menu (see the ﬁrst image below). After some experimentation, we settled on the WINDOW parameters shown in the middle image below. Once you’ve entered these WINDOW parameters, push the GRAPH button to produce the the graph of y = x2 − 6x − 3, as shown in the rightmost image below. We’re looking for solutions of x2 − 6x − 3 = 0, so we need to locate where the graph of y = x2 − 6x − 3 intercepts the x-axis. That is, we need to ﬁnd the zeros of y = x2 − 6x − 3. Select 2:zero from the CALC menu, move the cursor slightly to the left of the ﬁrst x-intercept and press ENTER in response to “Left bound.” Move the cursor slightly to the right of the ﬁrst x-intercept and press ENTER in response to “Right bound.” Leave the cursor where it sits and press ENTER in response to “Guess.” The calculator responds by ﬁnding the x-coordinate of the x-intercept, as shown in the ﬁrst image below. Repeat the process to ﬁnd the second x-intercept of y = x2 − 6x − 3 shown in the second image below. Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 494 Reporting the solution on your homework: Duplicate the image in your calculator’s viewing window on your homework page. Use a ruler to draw all lines, but freehand any curves. y 20 −0.464102 6.464102 x 10 −10 y = x2 − 6x − 3 −20 Comparing exact and calculator approximations. How well do the √ graphing calculator √ solutions compare with the exact solutions, x = 3 − 2 3 and x = 3 + 2 3? After entering each in the calculator, the comparison is excellent! 8.4 The Quadratic Formula 1. The integer pair 4, −7 has product ac = −28 and sum b = −3. Hence, this trinomial factors. x2 − 3x − 28 = 0 (x + 4)(x − 7) = 0 Second Edition: 2012-2013 8.4. THE QUADRATIC FORMULA 495 Now we can use the zero product property to write: x+4=0 x = −4 or x−7=0 x=7 Thus, the solutions are x = −4 or x = 7. Quadratic formula: Compare ax2 + bx + c = 0 and x2 − 3x − 28 = 0 and note that a = 1, b = −3, and c = −28. Next, replace each occurrence of a, b, and c in the quadratic formula with open parentheses. √ −b ± b2 − 4ac The quadratic formula. x= 2a −( ) ± ( )2 − 4( )( ) x= Replace a, b, and c with 2( ) open parentheses. Now we can substitute: 1 for a, −3 for b, and −28 for c. x= −(−3) ± (−3)2 − 4(1)(−28) 2(1) √ 9 + 112 x= 2 √ 3 ± 121 x= 2 3 ± 11 x= 2 3± Substitute: 1 for a, −3 for b, and −28 for c Simplify. Exponents, then multiplication. Simplify: 9 + 112 = 121. Simplify: √ 121 = 11. Note that because of the “plus or minus” symbol, we have two answers. 3 − 11 2 −8 x= 2 x = −4 x= or 3 + 11 2 14 x= 2 x=7 x= Note that these answers match the answers found using the ac-test to factor the trinomial. 3. The integer pair −3, −5 has product ac = 15 and sum b = −8. Hence, this trinomial factors. x2 − 8x + 15 = 0 (x − 3)(x − 5) = 0 Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 496 Now we can use the zero product property to write: x−3=0 x=3 or x−5=0 x=5 Thus, the solutions are x = 3 or x = 5. Quadratic formula: Compare ax2 + bx + c = 0 and x2 − 8x + 15 = 0 and note that a = 1, b = −8, and c = 15. Next, replace each occurrence of a, b, and c in the quadratic formula with open parentheses. √ −b ± b2 − 4ac The quadratic formula. x= 2a −( ) ± ( )2 − 4( )( ) x= Replace a, b, and c with 2( ) open parentheses. Now we can substitute: 1 for a, −8 for b, and 15 for c. x= −(−8) ± (−8)2 − 4(1)(15) 2(1) √ 64 − 60 x= 2 √ 8± 4 x= 2 8±2 x= 2 8± Substitute: 1 for a, −8 for b, and 15 for c Simplify. Exponents, then multiplication. Simplify: 64 − 60 = 4. Simplify: √ 4 = 2. Note that because of the “plus or minus” symbol, we have two answers. 8−2 2 6 x= 2 x=3 x= or 8+2 2 10 x= 2 x=5 x= Note that these answers match the answers found using the ac-test to factor the trinomial. 5. The integer pair 6, −8 has product ac = −48 and sum b = −2. Hence, this trinomial factors. x2 − 2x − 48 = 0 (x + 6)(x − 8) = 0 Second Edition: 2012-2013 8.4. THE QUADRATIC FORMULA 497 Now we can use the zero product property to write: x+6=0 x = −6 or x−8=0 x=8 Thus, the solutions are x = −6 or x = 8. Quadratic formula: Compare ax2 + bx + c = 0 and x2 − 2x − 48 = 0 and note that a = 1, b = −2, and c = −48. Next, replace each occurrence of a, b, and c in the quadratic formula with open parentheses. √ −b ± b2 − 4ac The quadratic formula. x= 2a −( ) ± ( )2 − 4( )( ) x= Replace a, b, and c with 2( ) open parentheses. Now we can substitute: 1 for a, −2 for b, and −48 for c. x= −(−2) ± (−2)2 − 4(1)(−48) 2(1) √ 4 + 192 x= 2 √ 2 ± 196 x= 2 2 ± 14 x= 2 2± Substitute: 1 for a, −2 for b, and −48 for c Simplify. Exponents, then multiplication. Simplify: 4 + 192 = 196. Simplify: √ 196 = 14. Note that because of the “plus or minus” symbol, we have two answers. 2 − 14 2 −12 x= 2 x = −6 x= or 2 + 14 2 16 x= 2 x=8 x= Note that these answers match the answers found using the ac-test to factor the trinomial. 7. The integer pair 6, −5 has product ac = −30 and sum b = 1. Hence, this trinomial factors. x2 + x − 30 = 0 (x + 6)(x − 5) = 0 Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 498 Now we can use the zero product property to write: x+6=0 or x−5=0 x = −6 x=5 Thus, the solutions are x = −6 or x = 5. Quadratic formula: Compare ax2 + bx + c = 0 and x2 + x − 30 = 0 and note that a = 1, b = 1, and c = −30. Next, replace each occurrence of a, b, and c in the quadratic formula with open parentheses. √ −b ± b2 − 4ac The quadratic formula. x= 2a −( ) ± ( )2 − 4( )( ) Replace a, b, and c with x= 2( ) open parentheses. Now we can substitute: 1 for a, 1 for b, and −30 for c. −(1) ± (1)2 − 4(1)(−30) x= Substitute: 1 for a, 1 for b, 2(1) and −30 for c √ −1 ± 1 + 120 x= Simplify. Exponents, then 2 multiplication. √ −1 ± 121 x= Simplify: 1 + 120 = 121. 2 √ −1 ± 11 x= Simplify: 121 = 11. 2 Note that because of the “plus or minus” symbol, we have two answers. −1 − 11 2 −12 x= 2 x = −6 x= or −1 + 11 2 10 x= 2 x=5 x= Note that these answers match the answers found using the ac-test to factor the trinomial. 9. Compare x2 − 7x − 5 = 0 with ax2 + bx + c = 0 and note that a = 1, b = −7, and c = −5. Replace each occurrence of a, b, and c with open parentheses to prepare the quadratic formula for substitution. √ −b ± b2 − 4ac x= Quadratic formula. Replace a, b, 2a −( ) ± ( )2 − 4( )( ) and c with open parentheses. x= 2( ) Second Edition: 2012-2013 8.4. THE QUADRATIC FORMULA 499 Substitute 1 for a, −7 for b, and −5 for c. −(−7) ± (−7)2 − 4(1)(−5) x= Substitute: 1 for a, 2(1) −7 for b, and −5 for c √ 7 ± 49 + 20 x= Exponent, then multiplication. √2 7 ± 69 x= Simplify. 2 11. Compare 2x2 + x − 4 = 0 with ax2 + bx + c = 0 and note that a = 2, b = 1, and c = −4. Replace each occurrence of a, b, and c with open parentheses to prepare the quadratic formula for substitution. √ −b ± b2 − 4ac Quadratic formula. Replace a, b, x= 2a −( ) ± ( )2 − 4( )( ) x= and c with open parentheses. 2( ) Substitute 2 for a, 1 for b, and −4 for c. −(1) ± (1)2 − 4(2)(−4) Substitute: 2 for a, x= 2(2) 1 for b, and −4 for c √ −1 ± 1 + 32 Exponent, then multiplication. x= 4 √ −1 ± 33 x= Simplify. 4 13. Compare x2 −7x−4 = 0 with ax2 +bx+c = 0 and note that a = 1, b = −7, and c = −4. Replace each occurrence of a, b, and c with open parentheses to prepare the quadratic formula for substitution. √ −b ± b2 − 4ac Quadratic formula. Replace a, b, x= 2a −( ) ± ( )2 − 4( )( ) and c with open parentheses. x= 2( ) Substitute 1 for a, −7 for b, and −4 for c. −(−7) ± (−7)2 − 4(1)(−4) x= Substitute: 1 for a, 2(1) −7 for b, and −4 for c √ 7 ± 49 + 16 x= Exponent, then multiplication. √2 7 ± 65 x= Simplify. 2 Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 500 15. Compare 4x2 −x−2 = 0 with ax2 +bx+c = 0 and note that a = 4, b = −1, and c = −2. Replace each occurrence of a, b, and c with open parentheses to prepare the quadratic formula for substitution. √ −b ± b2 − 4ac x= Quadratic formula. Replace a, b, 2a −( ) ± ( )2 − 4( )( ) and c with open parentheses. x= 2( ) Substitute 4 for a, −1 for b, and −2 for c. −(−1) ± (−1)2 − 4(4)(−2) x= Substitute: 4 for a, 2(4) −1 for b, and −2 for c √ 1 ± 1 + 32 Exponent, then multiplication. x= √8 1 ± 33 x= Simplify. 8 17. Compare x2 −x−11 = 0 with ax2 +bx+c = 0 and note that a = 1, b = −1, and c = −11. Replace each occurrence of a, b, and c with open parentheses to prepare the quadratic formula for substitution. √ −b ± b2 − 4ac Quadratic formula. Replace a, b, x= 2a −( ) ± ( )2 − 4( )( ) and c with open parentheses. x= 2( ) Substitute 1 for a, −1 for b, and −11 for c. −(−1) ± (−1)2 − 4(1)(−11) x= Substitute: 1 for a, 2(1) −1 for b, and −11 for c √ 1 ± 1 + 44 x= Exponent, then multiplication. √2 1 ± 45 x= Simplify. 2 √ In this case, note that we can factor out a perfect square, namely 9. √ √ 9 5 x= 2√ 1±3 5 x= 2 1± Second Edition: 2012-2013 √ √ √ 45 = 9 5. Simplify: √ 9=3 8.4. THE QUADRATIC FORMULA 501 19. Compare x2 −9x+9 = 0 with ax2 +bx+c = 0 and note that a = 1, b = −9, and c = 9. Replace each occurrence of a, b, and c with open parentheses to prepare the quadratic formula for substitution. √ −b ± b2 − 4ac x= Quadratic formula. Replace a, b, 2a −( ) ± ( )2 − 4( )( ) x= and c with open parentheses. 2( ) Substitute 1 for a, −9 for b, and 9 for c. −(−9) ± (−9)2 − 4(1)(9) x= Substitute: 1 for a, 2(1) −9 for b, and 9 for c √ 9 ± 81 − 36 x= Exponent, then multiplication. √2 9 ± 45 x= Simplify. 2 In this case, note that we can factor out a perfect square, namely √ √ 9 5 x= 2√ 9±3 5 x= 2 9± √ 9. √ √ √ 45 = 9 5. Simplify: √ 9=3 21. Compare x2 −3x−9 = 0 with ax2 +bx+c = 0 and note that a = 1, b = −3, and c = −9. Replace each occurrence of a, b, and c with open parentheses to prepare the quadratic formula for substitution. √ −b ± b2 − 4ac Quadratic formula. Replace a, b, x= 2a −( ) ± ( )2 − 4( )( ) x= and c with open parentheses. 2( ) Substitute 1 for a, −3 for b, and −9 for c. −(−3) ± (−3)2 − 4(1)(−9) x= Substitute: 1 for a, 2(1) −3 for b, and −9 for c √ 3 ± 9 + 36 x= Exponent, then multiplication. √2 3 ± 45 x= Simplify. 2 Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 502 In this case, note that we can factor out a perfect square, namely √ √ 9 5 2√ 3±3 5 x= 2 x= √ 3± 45 = √ 9. √ √ 9 5. Simplify: √ 9=3 23. Compare x2 − 7x − 19 = 0 with ax2 + bx + c = 0 and note that a = 1, b = −7, and c = −19. Replace each occurrence of a, b, and c with open parentheses to prepare the quadratic formula for substitution. x= x= −b ± −( √ b2 − 4ac 2a ) ± ( )2 − 4( 2( ) Quadratic formula. Replace a, b, )( ) and c with open parentheses. Substitute 1 for a, −7 for b, and −19 for c. x= −(−7) ± (−7)2 − 4(1)(−19) 2(1) √ 49 + 76 x= √2 7 ± 125 x= 2 7± Substitute: 1 for a, −7 for b, and −19 for c Exponent, then multiplication. Simplify. In this case, note that we can factor out a perfect square, namely √ √ 25 5 x= 2√ 7±5 5 x= 2 √ 25. √ √ √ 125 = 25 5. 7± Simplify: √ 25 = 5 25. Compare 12x2 + 10x − 1 = 0 with ax2 + bx + c = 0 and note that a = 12, b = 10, and c = −1. Replace each occurrence of a, b, and c with open parentheses to prepare the quadratic formula for substitution. x= x= −b ± −( √ b2 − 4ac 2a ) ± ( )2 − 4( 2( ) Second Edition: 2012-2013 Quadratic formula. Replace a, b, )( ) and c with open parentheses. 8.4. THE QUADRATIC FORMULA 503 Substitute 12 for a, 10 for b, and −1 for c. (10)2 − 4(12)(−1) 2(12) √ −10 ± 100 + 48 x= 24 √ −10 ± 148 x= 24 x= −(10) ± Substitute: 12 for a, 10 for b, and −1 for c Exponent, then multiplication. Simplify. In this case, note that we can factor out a perfect square, namely √ √ −10 ± 4 37 x= 24√ −10 ± 2 37 x= 24 √ 4. √ √ √ 148 = 4 37. Simplify: √ 4=2 Finally, notice that both numerator and denominator are divisible by 2. √ −10 ± 2 37 2 x= 24 2 √ −10 2 37 ± 2 2 x= 24 √2 −5 ± 37 x= 12 Divide numerator and denominator by 2. Distribute the 2. Simplify. 27. Compare 7x2 − 10x + 1 = 0 with ax2 + bx + c = 0 and note that a = 7, b = −10, and c = 1. Replace each occurrence of a, b, and c with open parentheses to prepare the quadratic formula for substitution. x= x= −b ± −( √ b2 − 4ac 2a ) ± ( )2 − 4( 2( ) Quadratic formula. Replace a, b, )( ) and c with open parentheses. Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 504 Substitute 7 for a, −10 for b, and 1 for c. x= −(−10) ± (−10)2 − 4(7)(1) 2(7) √ 100 − 28 14 √ 10 ± 72 x= 14 x= 10 ± Substitute: 7 for a, −10 for b, and 1 for c Exponent, then multiplication. Simplify. In this case, note that we can factor out a perfect square, namely √ √ 36 2 x= 14√ 10 ± 6 2 x= 14 √ 36. √ √ √ 72 = 36 2. 10 ± Simplify: √ 36 = 6 Finally, notice that both numerator and denominator are divisible by 2. √ 10 ± 6 2 2 x= 14 2 √ 10 6 2 ± 2 2 x= 14 2 √ 5±3 2 x= 7 Divide numerator and denominator by 2. Distribute the 2. Simplify. 29. Compare 2x2 − 12x + 3 = 0 with ax2 + bx + c = 0 and note that a = 2, b = −12, and c = 3. Replace each occurrence of a, b, and c with open parentheses to prepare the quadratic formula for substitution. x= x= −b ± −( √ b2 − 4ac 2a ) ± ( )2 − 4( 2( ) Second Edition: 2012-2013 Quadratic formula. Replace a, b, )( ) and c with open parentheses. 8.4. THE QUADRATIC FORMULA 505 Substitute 2 for a, −12 for b, and 3 for c. x= −(−12) ± 12 ± (−12)2 − 4(2)(3) 2(2) √ 144 − 24 √4 12 ± 120 x= 4 x= Substitute: 2 for a, −12 for b, and 3 for c Exponent, then multiplication. Simplify. In this case, note that we can factor out a perfect square, namely √ √ 4 30 x= 4√ 12 ± 2 30 x= 4 √ 4. √ √ √ 120 = 4 30. 12 ± Simplify: √ 4=2 Finally, notice that both numerator and denominator are divisible by 2. √ 12 ± 2 30 2 x= 4 2 √ 12 2 30 ± 2 2 x= 4 √2 6 ± 30 x= 2 Divide numerator and denominator by 2. Distribute the 2. Simplify. 31. Compare 13x2 − 2x − 2 = 0 with ax2 + bx + c = 0 and note that a = 13, b = −2, and c = −2. Replace each occurrence of a, b, and c with open parentheses to prepare the quadratic formula for substitution. x= x= −b ± −( √ b2 − 4ac 2a ) ± ( )2 − 4( 2( ) Quadratic formula. Replace a, b, )( ) and c with open parentheses. Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 506 Substitute 13 for a, −2 for b, and −2 for c. x= −(−2) ± (−2)2 − 4(13)(−2) 2(13) √ 4 + 104 x= 26 √ 2 ± 108 x= 26 2± Substitute: 13 for a, −2 for b, and −2 for c Exponent, then multiplication. Simplify. In this case, note that we can factor out a perfect square, namely √ √ 36 3 x= 26 √ 2±6 3 x= 26 √ 36. √ √ √ 108 = 36 3. 2± Simplify: √ 36 = 6 Finally, notice that both numerator and denominator are divisible by 2. √ 2±6 3 2 x= 26 2 √ 2 6 3 ± 2 2 x= 26 2√ 1±3 3 x= 13 Divide numerator and denominator by 2. Distribute the 2. Simplify. 33. When the object returns to ground level, its height y above ground level is y = 0 feet. To ﬁnd the time when this occurs, substitute y = 0 in the formula y = 240 + 160t − 16t2 and solve for t. y = 240 + 160t − 16t2 0 = 240 + 160t − 16t 2 Original equation. Set y = 0. Each of the coeﬃcients is divisible by 16. 0 = t2 − 10t − 15 Second Edition: 2012-2013 Divide both sides by −16. 8.4. THE QUADRATIC FORMULA 507 Compare t2 − 10t − 15 = 0 with at2 + bt + c = 0 and note that a = 1, b = −10, and c = −15. Replace each occurrence of a, b, and c with open parentheses to prepare the quadratic formula for substitution. Note that we are solving for t this time, not x. t= t= −b ± −( √ b2 − 4ac 2a ) ± ( )2 − 4( 2( ) Quadratic formula. Replace a, b, )( ) and c with open parentheses. Substitute 1 for a, −10 for b, and −15 for c. t= −(−10) ± 10 ± (−10)2 − 4(1)(−15) 2(1) √ 100 + 60 √2 10 ± 160 t= 2 t= Substitute: 1 for a, −10 for b, and −15 for c Exponent, then multiplication. Simplify. The answer is not in simple form, as we can factor out √ 16 10 t= 2√ 10 ± 4 10 t= 2 10 ± √ √ 16. √ √ √ 160 = 16 10. Simplify: √ 16 = 4 Use the distributive property to divide both terms in the numerator by 2. √ 10 4 10 t= ± Divide both terms by 2. 2 √ 2 Simplify. t = 5 ± 2 10 √ √ Thus, we have two solutions, t = 5 − 2 10 and t = 5 + 2 10. Use your calculator to ﬁnd decimal approximations. Thus: t ≈ −1.32455532 or t ≈ 11.3245532 Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 508 Rounding to the nearest tenth, t ≈ −1.3, 11.3. The negative time is irrelevant, so to the nearest tenth of a second, it takes the object approximately 11.3 seconds to return to ground level. 35. The manufacturer breaks even if his costs equal his incoming revenue. R=C Replace R with 6000x − 5x2 and C with 500000 + 5.25x. 6000x − 5x2 = 500000 + 5.25x The equation is nonlinear, so make one side equal to zero by moving all terms to one side of the equation. 0 = 5x2 + 5.25x − 6000x + 500000 0 = 5x2 − 5994.75x + 500000 Compare 5x2 − 5994.75x + 500000 = 0 with ax2 + bx + c = 0 and note that a = 5, b = −5994.75, and c = 500000. Replace each occurrence of a, b, and c with open parentheses to prepare the quadratic formula for substitution. √ −b ± b2 − 4ac x= 2a −( ) ± ( )2 − 4( )( ) x= 2( ) Substitute 5 for a, −5994.75 for b, and 500000 for c, then simplify. −(−5994.75) ± (−5994.75)2 − 4(5)(500000) x= 2(5) √ 5994.75 ± 35937037.56 − 10000000 x= 10 √ 5994.75 ± 25937027.56 x= 10 Enter each answer into your calculator. Second Edition: 2012-2013 8.4. THE QUADRATIC FORMULA 509 Thus, the solutions are x ≈ 90.19091857 x ≈ 1108.759081 or The ﬁrst answer rounds to 90 widgets, the second answer to 1109 widgets. 37. At the moment they are 60 miles apart, let t represent the time that Mike has been riding since noon. Because Todd started at 2 pm, he has been riding for two hours less than Mike. So, let t − 2 represent the number of hours that Todd has been riding at the moment they are 60 miles apart. Now, if Mike has been riding at a constant rate of 6 miles per hour for t hours, then he has travelled a distance of 6t miles. Because Todd has been riding at a constant rate of 8 miles per hour for t − 2 hours, he has travelled a distance of 8(t − 2) miles. 6t 60 8(t − 2) The distance and direction traveled by Mike and Todd are marked in the ﬁgure above. Note that we have a right triangle, so the sides of the triangle must satisfy the Pythagorean Theorem. That is, (6t)2 + [8(t − 2)]2 = 602 . Use the Pythagorean Theorem. Distribute the 8. (6t)2 + (8t − 16)2 = 602 Distribute the 8. Square each term. Use (a − b)2 = a2 − 2ab + b2 to expand (8t − 16)2 . 36t2 + 64t2 − 256t + 256 = 3600 2 100t − 256t + 256 = 3600 Square each term. Simplify: 36t2 + 64t2 = 100t2 The resulting equation is nonlinear. Make one side equal to zero. 100t2 − 256t − 3344 = 0 2 25t − 64t − 836 = 0 Subtract 3600 from both sides. Divide both sides by 4. Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 510 Compare 25t2 − 64t − 836 = 0 with at2 + bt + c = 0 and note that a = 25, b = −64, and c = −836. Replace each occurrence of a, b, and c with open parentheses to prepare the quadratic formula for substitution. Note that we are solving for t this time, not x. √ −b ± b2 − 4ac Quadratic formula. Replace a, b, t= 2a −( ) ± ( )2 − 4( )( ) t= and c with open parentheses. 2( ) Substitute 25 for a, −64 for b, and −836 for c. −(−64) ± (−64)2 − 4(25)(−836) t= Substitute: 25 for a, 2(25) −64 for b, and −836 for c √ 64 ± 4096 + 83600 Exponent, then multiplication. t= √ 50 64 ± 87696 t= Simplify. 50 Now, as the request is for an approximate time, we won’t bother with simple form and reduction, but proceed immediately to the calculator to approximate this last result. The negative time is irrelevant and discarded. Thus, Mike has been riding for approximately 7.202702086 hours. To change 0.202702086 hours to minutes, 0.202702086 hr = 0.202702086 hr × 60 min = 12.16212516 min hr Rounding to the nearest minute, Mike has been riding for approximately 7 hours and 12 minutes. Because Mike started riding at noon, the time at which he and Todd are 60 miles apart is approximately 7:12 pm. 39. We follow the Requirements for Word Problem Solutions. 1. Set up a variable dictionary. A carefully labeled ﬁgure will help us maintain our focus. We’ll let W represent the uniform width of the ﬁeld. Because the length is 7 feet longer than its width, the length is W + 7. Second Edition: 2012-2013 8.4. THE QUADRATIC FORMULA 511 A = 76 ft2 W W +7 2. Set up an equation. The area of the rectangular ﬁeld is found by multiplying the width and the length. Thus, Area = Width × Length 76 = W (W + 7) 3. Solve the equation. We start by expanding the right-hand side of the equation. 76 = W 2 + 7W The resulting equation is nonlinear. Make one side zero. 0 = W 2 + 7W − 76 Compare W 2 + 7W − 76 = 0 with aW 2 + bW + c = 0 and note that a = 1, b = 7, and c = −76. Replace each occurrence of a, b, and c with open parentheses to prepare the quadratic formula for substitution. Note that we are solving for W this time, not x. W = W = −b ± −( √ b2 − 4ac 2a ) ± ( )2 − 4( 2( ) Quadratic formula. Replace a, b, )( ) and c with open parentheses. Substitute 1 for a, 7 for b, and −76 for c. (7)2 − 4(1)(−76) W = 2(1) √ −7 ± 49 + 304 W = √2 −7 ± 353 W = 2 −(7) ± Substitute: 1 for a, 7 for b, and −76 for c Exponent, then multiplication. Simplify. Second Edition: 2012-2013 CHAPTER 8. QUADRATIC FUNCTIONS 512 Now, as the request is for an approximate time, we won’t bother with simple form and reduction, but proceed immediately to the calculator to approximate this last result. Enter the expression (-7-sqrt(353))(2) and press the ENTER key. Enter the expression (-7+sqrt(353))(2) and press the ENTER key. The results are W ≈ −12.894147114 or W ≈ 5.894147114. 4. Answer the question. The negative width is irrelevant and discarded. Thus, rounding to the nearest tenth of a foot, the width of the ﬁeld is 5.9 feet. Because the length is 7 feet longer than the width, the length of the ﬁeld is 12.9 feet. 5. Look back. Because we rounded to the nearest tenth of a foot, we don’t expect the answers to check exactly. A = 76 ft2 5.9 12.9 Note that (5.9)(12.9) = 76.11, which is very close to the given area. 41. Substitute the concentration C = 330 into the given equation. C = 0.01125t2 + 0.925t + 318 330 = 0.01125t2 + 0.925t + 318 The equation is nonlinear, so make one side equal to zero by subtracting 330 from both sides of the equation. 0 = 0.01125t2 + 0.925t − 12 Compare 0.01125t2 + 0.925t − 12 = 0 with at2 + bt + c = 0 and note that a = 0.01125, b = 0.925, and c = −12. Replace each occurrence of a, b, and c with open parentheses to prepare the quadratic formula for substitution. Note that we are solving for t this time, not x. √ −b ± b2 − 4ac W = 2a −( ) ± ( )2 − 4( )( ) W = 2( ) Second Edition: 2012-2013 8.4. THE QUADRATIC FORMULA 513 Substitute 0.01125 for a, 0.925 for b, and −12 for c, then simplify. (0.925)2 − 4(0.01125)(−12) W = 2(0.01125) √ −0.925 ± 0.855625 + 0.54 W = 0.0225 √ −0.925 ± 1.395625 W = 0.0225 −(0.925) ± Enter each answer into your calculator. Thus, the solutions are t ≈ −93.61625489 or t ≈ 11.39493267. The negative answer is irrelevant and is discarded. Remember, t represents the number of years after the year 1962. Rounding the second answer to the nearest year, the concentration reached a level of 330 parts per million 11 years after the year 1962, that is, in the year 1973. It is interesting to compare this answer with the actual data: ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/ co2_annmean_mlo.txt. Second Edition: 2012-2013