Find the sum S of the infinite series Σk=2∞ 18·(−1/3)ᵏ.
Sequences & series worksheet with answers
1.Easy
a = 18r = −1/3k₀ = 2
S =
2.Easy
The geometric sequence aₙ = 5·0.8ⁿ⁻¹ decreases. Find the first index n for which aₙ < 0.2.
a₁ = 5r = 0.8ε = 0.2
n =
3.Medium
Find the sum S = Σk=1∞ 2/(k(k + 2)).
ak = 2/(k(k + 2))
S =
4.Medium
Exactly one of the four series converges. Click it.
A: Σ 1/(4k + 7)B: Σ 1/(k(k + 4))C: Σ (3k + 1)/(k + 2)D: Σ (k + 5)/k²
- 1A: Σ 1/(4k + 7)
- 2B: Σ 1/(k(k + 4))
- 3C: Σ (3k + 1)/(k + 2)
- 4D: Σ (k + 5)/k²
5.Hard
Find the coefficient c₃ of (x − 4)³ in the Taylor series of f(x) = 1/x about a = 4.
f(x) = 1/xa = 4k = 3
c₃ =
6.Hard
Recognise the series and find its sum: S = Σk=1∞ k·(−0.5)ᵏ.
ak = k·(−0.5)ᵏ
S =
Answer key
- 1. S = 1.5
- 2. n = 16
- 3. S = 1.5
- 4. B: Σ 1/(k(k + 4))
- 5. c₃ = −0.003906
- 6. S = −0.2222
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