Find the sum S5 of the first 5 terms of the geometric sequence 0.5, 0.6, 0.72, …
Sequences & series worksheet with answers
1.Easy
a₁ = 0.5r = 1.2n = 5
S5 =
2.Easy
The geometric sequence aₙ = 2·0.5ⁿ⁻¹ decreases. Find the first index n for which aₙ < 0.1.
a₁ = 2r = 0.5ε = 0.1
n =
3.Medium
Apply the ratio test to Σk=1∞ 3ᵏ·k!/kᵏ. Find L = lim |ak+1/ak|.
ak = 3ᵏ·k!/kᵏ
L =
4.Medium
Exactly one of the four series diverges. Click it.
A: Σ (−1)ᵏ/√kB: Σ ln k / kC: Σ 1/(k(k + 1))D: Σ (3/5)ᵏ
- 1A: Σ (−1)ᵏ/√k
- 2B: Σ ln k / k
- 3C: Σ 1/(k(k + 1))
- 4D: Σ (3/5)ᵏ
5.Hard
Recognise the series and find its sum: S = Σk=1∞ k·0.25ᵏ.
ak = k·0.25ᵏ
S =
6.Hard
Find the coefficient c₄ of (x − 1)⁴ in the Taylor series of f(x) = ∛x about a = 1.
f(x) = ∛xa = 1k = 4
c₄ =
Answer key
- 1. S5 = 3.721
- 2. n = 6
- 3. L = 1.104
- 4. B: Σ ln k / k
- 5. S = 0.4444
- 6. c₄ = −0.04115
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