ga2k 10102 2.1dustintench.pbworks.com/f/ch.2skillspractice.pdf · what is the quadratic formula...
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Chapter 2 l Skills Practice 295
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Skills Practice Skills Practice for Lesson 2.1
Name _____________________________________________ Date ____________________
Quadratic Formula Deriving the Quadratic Formula
Vocabulary Answer each question.
1. What is the Quadratic Formula used to calculate?
2. What is the formula for the Quadratic Formula?
Problem Set Use the Quadratic Formula to calculate the root(s) of each quadratic equation. Check your answers.
1. x2 � 3x � 10 � 0 2. x2 � 7x � 8 � 0
a � 1, b � 3, c � �10
x � �b � √_________
b2 � 4ac ________________ 2a
� �3 � √
______________ 32 � 4(1)(�10) ____________________
2(1)
� �3 � √___
49 __________ 2
x � �3 � 7 _______ 2 or x � �3 � 7 _______
2
x � 4 __ 2 � 2 x � �10 _____
2 � �5
Check:
22 � 3(2) � 10 � 4 � 6 � 10 � 0
(�5)2 � 3(�5) � 10 � 25 � 15 � 10 � 0
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3. 2x2 � 4x � 2 � 0 4. �2x2 � 3x � 1 � 0
Use the Quadratic Formula to calculate the zero(s) of each quadratic function. Check your answers.
5. f(x) � x2 � 25 6. f(x) � 3x2 � 5x
Zeros: (�5, 0), (5, 0)
a � 1, b � 0, c � �25
x � �b � √_________
b2 � 4ac ________________ 2a
� �0 � √
______________ 02 � 4(1)(�25) ____________________
2(1)
� 0 � √____
100 _________ 2
x � 10 ___ 2 or x � �10 _____
2
x � 5 x � �5
Check:
(5)2 � 25 � 25 � 25 � 0
(�5)2 � 25 � 25 � 25 � 0
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Chapter 2 l Skills Practice 297
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Name _____________________________________________ Date ____________________
2
7. f(x) � (x � 7)2 � 30 8. f(x) � (x � 4)2 � 8
Use any method to solve each quadratic equation. Check your answers.
9. x2 � 6x � 9 � 0 10. x2 � 6x � 8 � 0
x2 � 6x � 9 � 0
( x � 3)( x � 3) � 0
x � 3
Check:
(3)2 � 6(3) � 9 � 9 � 18 � 9 � 0
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11. (x � 3)2 � 3 � 0 12. (x � 6)2 � 4 � 0
Use any method to calculate the zero(s) of each quadratic function. Check your answers.
Zeros: (10.27, 0), (2.73, 0)
x � �b � √_________
b2 � 4ac ________________ 2a
� �13 � √
________________ 132 � 4(�1)(�28) ________________________
2(�1)
� �13 � √___
57 ___________ �2
� 13 � √___
57 _________ 2
x � 13 � √___
57 _________ 2 or x � 13 � √
___ 57 _________
2
x � 10.27 x � 2.73 Check:
� ( 13 � √___
57 _________ 2
) 2 � 13 ( 13 � √___
57 _________ 2 ) � 28 � 0
� ( 13 � √___
57 _________ 2
) 2 � 13 ( 13 � √___
57 _________ 2 ) � 28 � 0
13. f(x) � �x2 � 13x � 28 14. f(x) � 2x2 � 8x � 42
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Chapter 2 l Skills Practice 299
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Name _____________________________________________ Date ____________________
2
15. f( x) � ( x � 4)2 � 9 16. f( x) � ( x � 7)2 � 25
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Chapter 2 l Skills Practice 301
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Skills Practice Skills Practice for Lesson 2.2
Name _____________________________________________ Date ____________________
Calculating Roots and Zeros Solving Quadratic Equations and Inequalities
Vocabulary Explain how each set of terms are related.
1. equation and inequality
2. roots of a quadratic equation and zeros of a quadratic function
Problem Set Use the Quadratic Formula to solve each quadratic equation. Check your solution.
1. x2 � 7x � 18 � 0
a � 1, b � 7, c � �18
x � �b � √_________
b2 � 4ac ________________ 2a
� �7 � √
______________ 72 � 4(1)(�18) ____________________
2(1) � �7 � √
________ 49 � 72 _______________
2 � �7 � √
____ 121 ___________
2
x � �7 � 11 ________ 2
or x � �7 � 11 ________ 2
x � 4 __ 2 � 2 x � �18 _____
2 � �9
Check:
22 � 7(2) � 18 � 4 � 14 � 18 � 0
(�9)2 � 7(�9) � 18 � 81 � 63 � 18 � 0
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2. x2 � 55x � 650 � 0
3. �2x2 � 3x � 7 � 0
4. 4x2 � x � 3 � 0
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Chapter 2 l Skills Practice 303
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Name _____________________________________________ Date ____________________
2
Use the Quadratic Formula to calculate the zeros of each quadratic function. Check your solution.
5. f(x) � �3x2 � 4x � 4
Zeros: ( � 2 __ 3
, 0 ) , (2, 0)
a � �3, b � 4, c � 4
x � �b � √_________
b2 � 4ac ________________ 2a
� �4 � √
_____________ 42 � 4(�3)(4) ___________________
2(�3) � �4 � √
________ 16 � 48 _______________
�6 � �4 � √
___ 64 __________
�6 � �4 � 8 _______
�6
x � � 2 __ 3 x � 2
Check:
�3 ( � 2 __ 3 ) 2 � 4 ( � 2 __
3 ) � 4 � � 4 __
3 � 8 __
3 � 4 � � 12 ___
3 � 4 � 0
�3(2)2 � 4(2) � 4 � �12 � 8 � 4 � 0
6. f(x) � 5x2 � 8x � 3
7. f(x) � 2x2 � 5x � 18
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8. f(x) � �3x2 � 7x � 2
Use the given information to answer each question.
9. A ball is tossed upward from a height of 1 meter with an initial velocity of 4 meters
per second. Its height can be modeled with the quadratic function h(t) � �5t2 � 4t � 1,
where t is the time in seconds and h is the height of the ball in meters t seconds after it
is thrown.
a. How long will it take the ball to reach its maximum height?
�b ____ 2a
� �4 ______ 2(�5)
� 4 ___ 10
� 0.4
The ball reaches its maximum height 0.4 second after it is thrown.
b. How long does it take for the ball to reach the ground?
h(t) � �5t2 � 4t � 1 � 0
a � �5, b � 4, c � 1
t � �b � √_________
b2 � 4ac ________________ 2a
� �4 � √
_____________ 42 � 4(�5)(1) ___________________
2(�5) �
�(4) � √________
16 � 20 ________________
�10 � �4 � √
___ 36 __________
�10 � �4 � 6 _______
�10
t � �0.2 or t � 1
The ball reaches the ground after 1 second.
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Chapter 2 l Skills Practice 305
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Name _____________________________________________ Date ____________________
2
10. A water balloon is thrown upward from a height of 10 feet with an initial velocity of
46 feet per second. Its height can be modeled with the quadratic function
h(t) � �16t2 � 46t � 10, where t is the time in seconds and h is the height of the
balloon in feet t seconds after it is thrown.
a. What is the maximum height the balloon reaches?
b. How long does it take for the balloon to reach the ground?
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11. A golf ball is thrown upward from a height of 5 feet with an initial velocity of 20 feet per
second. Its height can be modeled by the quadratic function h(t) � �16t2 � 20t � 5, where t
is the time in seconds and h is the height of the golf ball in feet t seconds after it is thrown.
a. How long will it take the golf ball to reach its maximum height?
b. How long will it take for the golf ball to reach the ground?
12. A soccer ball is thrown upward from a height of 4 meters with an initial velocity of 8 meters
per second. Its height can be modeled by the quadratic function h(t) � �5t2 � 8t � 4,
where t is the time in seconds and h is the height of the soccer ball in meters t seconds
after it is thrown.
a. How long will it take the soccer ball to reach its maximum height?
b. How long will it take for the soccer ball to reach the ground?
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Chapter 2 l Skills Practice 307
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Name _____________________________________________ Date ____________________
2
Use factoring to solve each quadratic inequality. Check your solution.
13. 2x2 � 5x � 5 � 2
2 x2 � 5x � 5 � 2
2 x2 � 5x � 7 � 0
(2 x � 7)( x � 1) � 0
(2 x � 7) � 0 or ( x � 1) � 0
2 x � �7 x � 1
x � �7 ___ 2
Try: x � �9, x � 0, and x � 2
2(�9)2 � 5(�9) � 5 � 2(81) � 45 � 5 � 112 112 � 2
2(0)2 � 5(0) � 5 � 0 � 0 � 5 � �5 �5 is not � �2
2(2)2 � 5(2) � 5 � 8 � 10 � 5 � 13 13 � 2
Solution: x � ( �∞, � 7 __ 2
] or x � [1, ∞)
14. 2 x2 � 14x � 27 � 7
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15. 4x2 � 15x � 25
16. 3x2 � 10x � �3
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Chapter 2 l Skills Practice 309
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Skills Practice Skills Practice for Lesson 2.3
Name _____________________________________________ Date ____________________
The DiscriminantThe Discriminant and the Nature of Roots/Vertex Form
Vocabulary Define each term or phrase in your own words.
1. number of zeros of a quadratic function
2. nature of the roots/zeros in a quadratic equation
3. discriminant
4. vertex form of a quadratic equation
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Problem Set Use the discriminant to determine the number and nature of the roots of each quadratic equation. Then solve for the root(s), if possible.
1. x2 � 5x � 7 � 0
a � 1, b � �5, c � 7
b2 � 4ac � (�5)2 � 4(1)(7) � 25 � 28 � �3
The equation has no roots because the discriminant is negative.
2. x2 � 8x � 3 � 0
3. 9x2 � 6x � 1 � 0
4. 5x2 � 2x � 1 � 0
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Chapter 2 l Skills Practice 311
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Name _____________________________________________ Date ____________________
2
Use the discriminant to determine the number of times the graph of each quadratic function intersects the x-axis. Calculate the x-intercepts.
5. f(x) � �2x2 � 7x � 3
a � �2, b � 7, c � 3
b2 � 4ac � 72 � 4(�2)(3) � 49 � 24 � 73
The graph of the function intercepts the x-axis two times.
x � �b � √_________
b2 � 4ac ________________ 2a
� �7 � √
_____________ 72 � 4(�2)(3) ___________________
2(�2) � �7 � √
___ 73 __________
�4
x � 3.886 or x � �0.386
x-intercepts approximately: (3.886, 0), (�0.386, 0)
6. f( x) � 2x2 � 4x � 2
7. f( x) � �2x2 � 8x � 42
8. f( x) � �5x2 � 10x � 5
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Write each equation in vertex form. Then determine the vertex. Check your solution.
9. y � x2 � 4x � 7 10. y � x2 � 8x � 12
y � ( x2 � 4x � 4) � 7 � 4
y � ( x � 2)2 � 11
Vertex: (2, �11)
Check:
�b ____ 2a
� 4 ____ 2(1)
� 2
y � (2)2 � 4(2) � 7
y � 4 � 8 � 7 � �11
11. y � 3x2 � 18x � 5 12. y � 2x2 � 8x � 9
13. y � x2 � 3x � 28 14. y � x2 � 17x � 74
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Chapter 2 l Skills Practice 313
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Skills Practice Skills Practice for Lesson 2.4
Name _____________________________________________ Date ____________________
The Complete Number SystemOperations with Complex Numbers
Vocabulary Write the term that best completes each statement.
1. Calculating the of a complex number can be accomplished by
repeated multiplication.
2. The of a complex number is used to divide complex numbers.
Problem Set Write the conjugate for each complex number.
1. �6 � 12 i 2. a � bi
�6 � 12 i
3. 2 i 4. �3 � 10i
5. 16 � 12 i 6. �4 � 4i
7. �a � bi 8. �1 � 8i
9. �5 � i 10. �13i
Calculate each sum.
11. (�3 � i ) � (4 � 2 i ) 12. (8 � 12 i ) � (6 � 14i )
1 � 3i
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13. (9 � 3i ) � (7 � 3i ) 14. (�7 � 5i ) � (1 � 10i )
15. (8 � 2 i ) � (�4 � 2 i ) 16. (�7 � 5i ) � (7 � i )
Calculate each difference.
17. (�3 � i ) � (4 � 2 i ) 18. (8 � 12 i ) � (6 � 14i )
�7 � i
19. (9 � 3i ) � (7 � 3i ) 20. (�7 � 5i ) � (1 � 10i )
21. (8 � 2 i ) � (�4 � 2 i ) 22. (�7 � 5i ) � (7 � i )
Calculate each product.
23. (�3 � i )(4 � 2 i )
� �12 � 6i � 4i � 2 i 2 � �12 � 2 i � 2 � �14 � 2 i
24. (8 � 12 i )(6 �14i )
25. (9 � 3i )(7 � 3i )
26. (�7 � 5i )(1 � 10i )
27. (8 � 2 i )(�4 � 2 i )
28. (�7 � 5i )(7 � i )
29. (2 � 3i )(2 � 3i )
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Chapter 2 l Skills Practice 315
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Name _____________________________________________ Date ____________________
2
30. (�6 � 4i )(�6 � 4i )
31. (10 � 10i )(10 � 10i )
32. (a � bi )(a � bi )
Calculate each quotient.
33. 9 � 2 i ______ 3 � 4i
9 � 2 i ______ 3 � 4i
� ( 9 � 2 i ______ 3 � 4i
) ( 3 � 4i ______ 3 � 4i
) � 27 � 36i � 6i � 8i 2 ___________________ 9 � 12 i � 12 i � 16i 2
� 27 � 30i � 8 ____________ 9 � 16
� 35 � 30i ________ 25
� 35 ___ 25
� 30i ___ 25
� 7 __ 5 � 6 __
5 i
34. 6 � 2 i ______ 8i
35. 3 � 6i ______ 4 � i
36. 8 � 5i _______ 10 � 2 i
Calculate the power of each complex number.
37. (�3 � 4i )3
� (�3 � 4i )(�3 � 4i )(�3 � 4i ) � (9 � 12 i � 12 i � 16i 2)(�3 � 4i )
� (9 � 24i � 16)(�3 � 4i ) � (�7 � 24i )(�3 � 4i ) � 21 � 28i � 72 i � 96i 2
� 21 � 44i � 96 � 117 � 44i
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38. (5 � i )3
39. (6 � 2i)3
40. (4 � 3i)3
Calculate the square root of each complex number.
41. √______
8 � 6i 42. √_______
5 � 12 i
√______
8 � 6i � a � bi
8 � 6i � (a2 � b2) � 2abi
8 � a2 � b2 and 6i � 2abi
a � 3 __ b
8 � ( 3 __ b
) 2 � b2
8 � 9 __ b2 � b2
8b2 � 9 � b4
b4 � 8b2 � 9 � 0
(b2 � 9)(b2 � 1) � 0
b2 � �9 or b2 � 1
b2 � 1
b � �1
a � 3 ___ �1
� �3
√______
8 � 6i � 3 � i or �3 � i
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2
43. √________
�3 � 4i 44. √________
�6 � 8i
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Skills Practice Skills Practice for Lesson 2.5
Name _____________________________________________ Date ____________________
Complex Roots and ZerosComplex Roots and Simplifying Complex Roots
Vocabulary The types of solutions of a quadratic equation are shown. Match each solution to the form of its corresponding equation’s discriminant.
1. two distinct real solutions a. b2 � 4ac � 0
2. one real solution b. b2 � 4ac � 0
3. two distinct complex solutions c. b2 � 4ac � 0
Problem Set Calculate the coordinates of the vertex and the x-intercepts for each quadratic function.
1. f(x) � x2 � 4x � 2
a � 1, b � �4, c � 2
x � �b ____ 2a
� �(�4)
______ 2(1)
� 2
f(2) � 22 � 4(2) � 2
� 4 � 8 � 2
� �2
Vertex: (2, �2)
x-intercepts: (2 � 2 √__
2 , 0), (2 � 2 √__
2 , 0)
x � �b � √_________
b2 � 4ac ________________ 2a
� �(�4) � √
______________ (�4)2 � 4(1)(2) _______________________
2(1)
� 4 � √_______
16 � 8 ____________ 2
� 4 � √__
8 _______ 2 � 4 � 2 √
__ 2 ________
2
� 2 � √__
2 , 2 � √__
2
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2. f(x) � 0.5x2 � 7x � 12
3. f(x) � 2x2 � x � 6
4. f(x) � x2 � 2x � 8
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Name _____________________________________________ Date ____________________
2
Use imaginary numbers to simplify each square root expression.
5. √_____
�27 6. √______
�400
� √_________
(�3)(3)(3)
� 3 √__
3 i
7. √______
�169 8. √_____
�54
Calculate the coordinates of the vertex and the complex zeros of each quadratic function. Check your solution.
9. f(x) � x2 � 4x � 13
a � 1, b � �4, c � 13 x � �b � √________
b2 – 4ac _______________ 2a
x � �b ____ 2 a
� �(�4)
______ 2(1)
� 2 � �(�4) � √
_______________ (�4)2 � 4(1)(13) ________________________
2(1)
f(2) � 22 � 4(2) � 13 � 4 � √________
16 � 52 _____________ 2
� 4 � 8 � 13 � 4 � √_____
�36 __________ 2 � 4 � 6i ______
2
� 9 x � 2 � 3i or x � 2 � 3i
Vertex: (2, 9) Zeros: x � 2 � 3i or x � 2 � 3i
Check:
f(2 � 3i) � (2 � 3i)2 � 4(2 � 3i) � 13
� (4 � 6i � 6i � 9i2) � 8 � 12i � 13
� 4 � 12i � 9 � 8 � 12i � 13
� 4 � 9 � 8 � 13 � 12i � 12i
� 0
f(2 � 3i) � (2 � 3i)2 � 4(2 � 3i) � 13
� (4 � 6i � 6i � 9i2) � 8 � 12i � 13
� 4 � 12i � 9 � 8 � 12i � 13
� 4 � 9 � 8 � 13 � 12i � 12i
� 0
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10. f(x) � �2x2 � 2x � 25
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Name _____________________________________________ Date ____________________
2
11. f(x) � 2x2 � 6x � 9
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12. f(x) � x2 � 4x � 8
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Name _____________________________________________ Date ____________________
2
Calculate the complex roots of each quadratic equation. Check your solution.
13. x2 � 2x � 5 � 0
a � 1, b � �2, c � 5 Check:
x � �b � √_________
b2 � 4ac ________________ 2a
(1 � 2 i)2 � 2(1 � 2 i) � 5
� �(�2) � √
______________ (�2)2 � 4(1)(5) _______________________
2(1) � (1 � 2 i � 2 i � 4 i2) � 2 � 4i � 5
� 2 � √_______
4 � 20 ____________ 2 � 1 � 4i � 4 � 2 � 4i � 5
� 2 � √_____
�16 __________ 2 � 2 � 4i ______
2 � 1 � 4 � 2 � 5 � 4i � 4i
� 1 � 2 i � 0
(1 � 2i)2 � 2(1 � 2i) � 5
� (1 � 2i � 2i � 4i2) � 2 � 4i � 5
� 1 � 4i � 4 � 2 � 4i � 5
� 1 � 4 � 2 � 5 � 4i � 4i
� 0
14. x2 � x � 1 � 0
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15. f(x) � �2x2 � 2x � 1
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Name _____________________________________________ Date ____________________
2
16. f(x) � �x2 � 5x � 7
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Skills Practice Skills Practice for Lesson 2.6
Name _____________________________________________ Date ____________________
Cases, Roots, and GraphsSolving Quadratic Inequalities
Vocabulary Describe how to solve a quadratic inequality using each of the given methods.
1. The Case Method
2. The Roots Method
3. The Graphing Method
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Problem Set For each quadratic function in factored form, show when f( x) � 0 and when f( x) � 0.
1. f(x) � (x � 1)(x � 2)
f( x) � 0
Case 1: x � 1 � 0 and x � 2 � 0
So, x � �1 and x � �2.
Case 2: x � 1 � 0 and x � 2 � 0
So, x � �1 and x � �2.
f( x) � 0
Case 1: x � 1 � 0 and x � 2 � 0
So, x � �1 and x � �2.
Case 2: x � 1 � 0 and x � 2 � 0
So, x � �1 and x � �2.
2. f(x) � (x � 3)(x � 4)
3. f(x) � (2x � 5)(x � 7)
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Name _____________________________________________ Date ____________________
2
4. f(x) � (x � 4)(4x � 3)
Solve each quadratic inequality using the case method.
5. x2 � 3x � 0
x( x � 3) � 0
Case 1: Both factors are positive. Case 2: Both factors are negative.
x � 0 and x � 3 � 0 x � 0 and x � 3 � 0
x � 3 x � 3
x � 3 x � 0
Solution: x � 0 or x � 3
6. x2 � x � 12
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7. 3x2 � � x � 4
8. x2 � 5x � 2 � 16
Solve each quadratic inequality using the roots method.
9. x2 � 8x � 1 � 0
a � 1, b � �8, c � 1 Try: x � 0, 1, 10
x � �b � √_________
b2 � 4ac ________________ 2a
02 � 8(0) � 1 � 0 � 0 � 1 � 1 is NOT � 0
� �(�8) � √
______________ (�8)2 � 4(1)(1) ________________________
2(1) 12 � 8(1) � 1 � 1 � 8 � 1 � �6 � 0
� 8 � √___
60 ________ 2 � 4 � √
___ 15 102 � 8(10) � 1 � 100 � 80 � 1 � 21 is NOT � 0
x � 0.127, 7.873 Approximate Solution: 0.127 � x � 7.873
Exact Solution: 4 � √___
15 � x � 4 � √___
15
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Name _____________________________________________ Date ____________________
2
10. �2 x2 � 8 � 6x
11. �3x2 � 10x � 0
12. x2 � 7x � 1 � 9
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Solve each quadratic inequality using the graphing method.
13. x2 � 4x � 12 y
86 102 4
2
−4
−2
−6
−8
−10
−12
−14
−16
−18
−2−4−6−8−10x
0 x-intercepts:
x2 � 4x � 12 � 0
( x � 2)( x � 6) � 0
x � 2 � 0 or x � 6 � 0
x � �2 x � 6
The portion of the parabola between the x-intercepts has y-values less than zero.
Solution: �2 � x � 6
14. � x2 � 3x � 4 � 0
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Chapter 2 l Skills Practice 335
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Name _____________________________________________ Date ____________________
2
15. x2 � 8x � 0
16. 2 x2 � 5x � 3
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Skills Practice Skills Practice for Lesson 2.7
Name _____________________________________________ Date ____________________
Carl Friedrich Gauss: Child ProdigyArithmetic Sequences, Series, and Their Partial Sums
Vocabulary Explain how each set of terms is related by identifying their similarities and differences.
1. explicit formula and recursive formula
2. finite series and infinite series
3. arithmetic sequence and arithmetic series
Problem Set List the next three terms in each sequence and identify the common difference, d.
1. 7, 12, 17, 22, 27, 32, 37; d � 5
2. 1, �1, �3, �5
3. 6.4, 7.6, 8.8, 10
4. �7, �4, �1
5. �2, �8, �14, �20
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6. 8.5, 7, 5.5, 4
7. 3 __ 5 , 4 __
5 , 1, 6 __
5
8. 4, 17, 30, 43
Write an explicit formula for each sequence.
9. 9, 20, 31, 42, . . . 10. 16, 7, �2, �11, . . .
an � 11(n � 1) � 9
an � 11n � 11 � 9
an � 11n � 2
11. 33, 24, 15, 6, . . . 12. 13, 16, 19, 22, . . .
13. 6.4, 7.6, 8.8, 10, . . . 14. 100, 105, 110, 115, 120, . . .
Use the explicit formula to calculate a50.
15. an � 3n � 25 16. a
n � �2.5n � 14
3(50) � 25 � 150 � 25 � 175
17. an � �10n � 14 18. a
n � 1 __
2 n � 6
Write a recursive formula for each sequence.
19. 5, 7, 9, 11, . . . 20. 4, 7, 10, 13, . . .
an � an�1 � 2, a1 � 5
21. 12, 7, 2, �3, . . . 22. 4, 2, 0, �2, . . .
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Name _____________________________________________ Date ____________________
2
23. 8.6, 7.3, 6, 4.7, . . . 24. 1 __ 3 , 1 __
6 , 0, � 1 __
6 , . . .
Use the explicit formula to calculate the first four terms of each arithmetic sequence.
25. an � 4n � 3 26. a
n � 1 __
3 (n � 1) � 6
7, 11, 15, 19
27. an � �2(n � 1) � 5 28. a
n � �6n � 20
29. an � 100(n � 1) � 50 30. a
n � �2n � 5
Use the recursive formula to calculate the first four terms of each arithmetic sequence.
31. an � a
n�1 � 9, a
1 � 6 32. a
n � a
n�1 � 9, a
1 � 6
6, �3, �12, �21
33. an � a
n�1 � 10, a
1 � 5 34. a
n � a
n�1 � 6, a
1 � 15
Write a recursive formula for each arithmetic sequence defined explicitly.
35. an � �5n � 20 36. a
n � n � 8
an � an�1 � 5, a1 � 15
37. an � 3(n � 1) � 2 38. a
n � 6(n � 1) � 3
39. an � �4(n � 1) � 1 40. a
n � �10(n � 1) � 25
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Write an explicit formula for each arithmetic sequence defined recursively.
41. an � a
n�1 � 6, a
1 � 20 42. a
n � a
n�1 � 19, a
1 � 1
an � 6(n � 1) � 20 � 6n � 14
43. an � a
n�1 � 2.4, a
1 � 4 44. a
n � a
n�1 � 3.5, a
1 � 7
Calculate each indicated sum for the given series.
4 5. 9 � 15 � 21 � 27 � 33 � 39 � 45
S4 � 72
S6 � 144
S � 189
46. 2 � 4 � 6 � 8 � 10 � 12 � 14 � 16 � 18 � 20
S4 �
S10
�
S �
47. (�3) � (�5) � (�7) � (�9) � (�11) � (�13)
S2 �
S4 �
S �
48. (�15) � (�10) � (�5) � 0 � 5 � 10 � 15
S2 �
S5 �
S �
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Chapter 2 l Skills Practice 341
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Name _____________________________________________ Date ____________________
2
Use the explicit formula for the sequence to write a formula for each series using sigma notation.
49. 0 � 3 � 6 � 9 � 12 � 15
� i�1
6
(3i � 3)
50. (�7) � (�5) � (�3) � (�1) � 1
51. 19 � 14 � 9 � 4 � (�1) � (�6) � (�11) � (�16) � (�21) � (�26)
52. 100 � 90 � 80 � 70 � 60 � 50 � 40 � 30
Calculate the sum of the arithmetic series.
53. 9 � 17 � 25 � 33 � 41 � 49 � 57
S � 7(9 � 57)
_________ 2
� 7(66)
_____ 2 � 462 ____
2 � 231
54. 19 � 14 � 9 � 4 � (�1) � (�6) � (�11) � (�16) � (�21) � (�26)
55. (�36) � (�29) � (�22) � (�15) � (�8) � (�1) � 6 � 13 � 20 � 27 � 34
56. 0 � 1 __ 4 � 1 __
2 � 3 __
4 � 1 � 5 __
4 � 3 __
2 � 7 __
4 � 2 � 9 __
4 � 5 __
2 � 11 ___
4 � 3
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342 Chapter 2 l Skills Practice
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Chapter 2 l Skills Practice 343
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Skills Practice Skills Practice for Lesson 2.8
Name _____________________________________________ Date ____________________
Mathematics Empowers Us To Do Superhuman Mental Calculations!Modeling Partial Sums of Arithmetic Series with Quadratic Equations
Vocabulary Describe how to calculate the sum of the first n odd or even integers using each method.
1. Gauss’s Solution
2. a function
Problem Set Write an explicit formula for each arithmetic sequence.
1. 2, 8, 14, 20, 26, . . . 2. �5, �1, 3, 7, 11, . . .
an � 6(n � 1) � 2
an � 6n � 6 � 2
an � 6n � 4
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344 Chapter 2 l Skills Practice
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3. 43, 36, 29, 22, 15, . . . 4. 50, 45.5, 41, 36.5, 32, . . .
Write a function to represent the sum of the first n terms of each arithmetic sequence with the given explicit formula.
5. an � 6n � 4 6. a
n � 4n � 7
a1 � 2
Sn � n(a1 � an) _________
2
� n __ 2 (2 � 6n � 4)
� n __ 2 (6n � 2)
Sn � 3n2 � n
7. an � �n � 3 8. a
n � �8n � 8
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Chapter 2 l Skills Practice 345
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Name _____________________________________________ Date ____________________
2
Calculate the sum of the first 20 terms of each arithmetic sequence by writing an explicit formula and using Gauss’s Solution method.
9. �11, �13, �15, �17, . . . 10. 9, 8, 7, 6, 5, . . .
an � �2n � 9
a1 � �11
a20 � �2(20) � 9 � �40 � 9 � �49
Sn � n(a1 � an) __________
2
S20 � 20(�11 � 49)
_____________ 2
S20 � 20(�60)
________ 2
S20 � �600
11. �5, 10, 25, 40, . . . 12. 12, 24, 36, 48, . . .
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346 Chapter 2 l Skills Practice
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Write a function to represent the sum of the first n terms of each arithmetic sequence with the given explicit formula. Use the function to calculate the sum of the first 100 terms of the sequence.
13. an � 3n � 5
a1 � �2
Sn � n(a1 � an) __________
2
� n __ 2 (�2 � 3n � 5)
� n __ 2 (3n � 7)
Sn � 3 __ 2 n2 � 7 __
2 n
Sn � 3 __ 2 n2 � 7 __
2 n
S100 � 3 __ 2 (100)2 � 7 __
2 (100)
S100 � 3 __ 2 (10,000) � 7 __
2 (100)
S100 � 15,000 � 350
S100 � 14,650
14. an � �2n � 26
15. an � 4n � 7
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Chapter 2 l Skills Practice 347
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Name _____________________________________________ Date ____________________
2
16. an � �5n � 2
The first four figures in a block pattern of 100 figures are given. Use the figures to answer the questions.
17.
a. Write a sequence to represent the number of new blocks used in each figure.
1, 3, 5, 7, . . .
b. Write an explicit formula to calculate any term of the sequence.
an � 2(n � 1) � 1
an � 2n � 1
c. Find the 100th term in the sequence.
a100 � 2(100) � 1 � 199
d. Calculate the total number of new blocks used in the 10th figure.
a10 � 2(10) � 1 � 19
Sn � n(a1 � an) _________
2
S10 � 10(1 � 19)
__________ 2
S10 � 100
There are 100 new blocks in the 10th figure.
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348 Chapter 2 l Skills Practice
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18.
a. Write a sequence to represent the number of new blocks used in each figure.
b. Write an explicit formula to calculate any term of the sequence.
c. Find the 100th term in the sequence.
d. Calculate the total number of new blocks used in the 10th figure.
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Chapter 2 l Skills Practice 349
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19.
a. Write a sequence to represent the number of new marbles used in each figure.
b. Write an explicit formula to calculate any term of the sequence.
c. Find the 100th term in the sequence.
d. Calculate the total number of new marbles used in the 10th figure.
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350 Chapter 2 l Skills Practice
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20.
a. Write a sequence to represent the number of new marbles used in each figure.
b. Write an explicit formula to calculate any term of the sequence.
c. Find the 100th term in the sequence.
d. Calculate the total number of new marbles used in the 10th figure.