Find the sum S7 of the first 7 terms of the geometric sequence 4, −12, 36, …
Sequences & series worksheet with answers
1.Easy
a₁ = 4r = −3n = 7
S7 =
2.Easy
Find the sum S9 of the first 9 terms of the geometric sequence 1, 2, 4, …
a₁ = 1r = 2n = 9
S9 =
3.Medium
Exactly one of the four series diverges. Click it.
A: Σ (−1)ᵏ/kB: Σ k²/3ᵏC: Σ 1/(k(k + 3))D: Σ (4k + 1)/(k + 2)
- 1A: Σ (−1)ᵏ/k
- 2B: Σ k²/3ᵏ
- 3C: Σ 1/(k(k + 3))
- 4D: Σ (4k + 1)/(k + 2)
4.Medium
Exactly one of the four series converges. Click it.
A: Σ 1/(3k + 5)B: Σ (3k + 1)/(k + 2)C: Σ (k + 2)/k²D: Σ k²/2ᵏ
- 1A: Σ 1/(3k + 5)
- 2B: Σ (3k + 1)/(k + 2)
- 3C: Σ (k + 2)/k²
- 4D: Σ k²/2ᵏ
5.Hard
Find the coefficient c₂ of (x − 1)² in the Taylor series of f(x) = e2x about a = 1.
f(x) = e2xa = 1k = 2
c₂ =
6.Hard
Recognise the series and find its sum: S = Σk=0∞ (−1)ᵏ/(2k)!.
ak = (−1)ᵏ/(2k)!
S =
Answer key
- 1. S7 = 2188
- 2. S9 = 511
- 3. D: Σ (4k + 1)/(k + 2)
- 4. D: Σ k²/2ᵏ
- 5. c₂ = 14.78
- 6. S = 0.5403
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