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Chapter 12 Sequences; Induction; the Binomial Theorem

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<strong>Chapter</strong> <strong>12</strong> Review Exercises<br />

29.<br />

7<br />

∑<br />

k = 1<br />

10<br />

30. ∑ ( )<br />

k = 1<br />

⎛<br />

7<br />

⎞ ⎛<br />

7<br />

⎞<br />

⎛1⎞ ⎛1⎞<br />

k ⎜1−<br />

1<br />

1 1<br />

⎜ ⎟ ⎟ ⎜ −<br />

3 1<br />

⎜ ⎟ ⎟<br />

⎛ ⎞ ⎜ ⎝ ⎠ ⎟ ⎜ ⎝3⎠<br />

⎟<br />

⎜ ⎟ = =<br />

⎝3⎠ 3⎜ 1 ⎟ 3⎜ 2 ⎟<br />

1−<br />

⎛ ⎞<br />

⎜ 3 ⎟ ⎜ ⎜ ⎟<br />

3 ⎟<br />

⎝ ⎠ ⎝ ⎝ ⎠ ⎠<br />

1⎛<br />

1 ⎞<br />

= ⎜1−<br />

⎟<br />

2 ⎝ 2187 ⎠<br />

1 2186 1093<br />

= ⋅ = ≈0.49977<br />

2 2187 2187<br />

( )<br />

⎛<br />

10<br />

k 1− −2 ⎞<br />

⎛1−1024<br />

⎞<br />

− 2 = − 2⎜<br />

⎟=−2<br />

⎜<br />

⎜ ⎟<br />

1 −( −2) ⎟ 3<br />

⎝ ⎠<br />

⎝ ⎠<br />

2<br />

=− ( − 1023)<br />

= 682<br />

3<br />

31. Arithmetic<br />

a = 3, d = 4, a = a + ( n−<br />

1) d<br />

1 n 1<br />

a 9 = 3 + (9 − 1)4 = 3+ 8(4) = 3+ 32 = 35<br />

32. Arithmetic<br />

a = 1, d = − 2, a = a + ( n−1)<br />

d<br />

1 n 1<br />

a 8 = 1 + (8−1)( − 2) = 1+ 7( − 2) = 1− 14 = −13<br />

33. Geometric<br />

1<br />

n 1<br />

a1 = 1, r = , n = 11; an<br />

= a1r −<br />

10<br />

a<br />

11<br />

11−1 10<br />

⎛ 1 ⎞ ⎛ 1 ⎞<br />

= 1⋅ ⎜ ⎟ = ⎜ ⎟<br />

⎝ 10 ⎠ ⎝ 10 ⎠<br />

1<br />

=<br />

10,000,000,000<br />

34. Geometric<br />

n<br />

a = 1, r = 2, n= 11; a = a r −<br />

1 n 1<br />

11−1 10<br />

( ) ( )<br />

a 11 = 1⋅ 2 = 2 = 1024<br />

35. Arithmetic<br />

a = 2, d = 2, n = 9, a = a + ( n−<br />

1) d<br />

1 n 1<br />

a 9 = 2 + (9− 1) 2 = 2+<br />

8 2<br />

= 9 2 ≈<strong>12</strong>.7279<br />

36. Geometric<br />

n<br />

a = 2, r = 2, n= 9, a = a r −<br />

1 n 1<br />

−<br />

( ) ( )<br />

9 1 8<br />

a9 = 2 2 = 2 2 = 2⋅16<br />

= 16 2 ≈ 22.6274<br />

1<br />

1<br />

37. 7 1 20 1<br />

a = a + 6d = 31 a = a + 19d<br />

= 96;<br />

Solve <strong>the</strong> system of equations:<br />

a + 6d<br />

= 31<br />

1<br />

a1<br />

+ 19d<br />

= 96<br />

Subtract <strong>the</strong> second equation from <strong>the</strong> first<br />

equation and solve for d.<br />

− 13d<br />

=−65<br />

d = 5<br />

a 1 = 31− 6(5) = 31− 30 = 1<br />

a = a + n−<br />

d<br />

n<br />

( )<br />

( n )( )<br />

1 1<br />

= 1+ −1 5<br />

= 1+ 5n<br />

−5<br />

= 5n<br />

−4<br />

General formula: { a } = { 5n−<br />

4}<br />

38. 8 1 17 1<br />

n<br />

a = a + 7d =− 20 a = a + 16d<br />

= − 47;<br />

Solve <strong>the</strong> system of equations:<br />

a + 7d<br />

=−20<br />

1<br />

a1<br />

+ 16d<br />

=−47<br />

Subtract <strong>the</strong> second equation from <strong>the</strong> first<br />

equation and solve for d.<br />

− 9d<br />

= 27<br />

d = −3<br />

a 1 = −20 −7( − 3) = − 20 + 21 = 1<br />

a = a + n−<br />

d<br />

n<br />

( )<br />

( n )( )<br />

1 1<br />

= 1+ −1 −3<br />

= 1− 3n<br />

+ 3<br />

=− 3n<br />

+ 4<br />

General formula: { a } = { − 3n+<br />

4}<br />

39. 10 1 18 1<br />

a = a + 9d = 0 a = a + 17d<br />

= 8;<br />

Solve <strong>the</strong> system of equations:<br />

a + 9d<br />

= 0<br />

1<br />

a1<br />

+ 17d<br />

= 8<br />

Subtract <strong>the</strong> second equation from <strong>the</strong> first<br />

equation and solve for d.<br />

− 8d<br />

=−8<br />

d = 1<br />

a 1 = − 9(1) = − 9<br />

a = a + n−<br />

d<br />

n<br />

( )<br />

( n )( )<br />

1 1<br />

=− 9+ −1 1<br />

=− 9+ n −1<br />

= n −10<br />

General formula: { a } = { n−<br />

10}<br />

n<br />

n<br />

<strong>12</strong>75<br />

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