The geometric sequence aₙ = 8·0.75ⁿ⁻¹ decreases. Find the first index n for which aₙ < 0.2.
Sequences & series worksheet with answers
1.Easy
a₁ = 8r = 0.75ε = 0.2
n =
2.Easy
A ball is dropped and its first rebound reaches 10 m. Every next rebound reaches 85% of the previous one. Which rebound n is the first one lower than 0.01 m?
a₁ = 10r = 0.85ε = 0.01
n =
3.Medium
Find the sum S = Σk=137 2/(k(k + 1)).
ak = 2/(k(k + 1))n = 37
S =
4.Medium
Find the radius of convergence R of the power series Σk=1∞ 25ᵏx²ᵏ/k.
Σ 25ᵏx²ᵏ/kx₀ = 0
R =
5.Hard
Find the coefficient c₂ of (x − 4)² in the Taylor series of f(x) = 1/x about a = 4.
f(x) = 1/xa = 4k = 2
c₂ =
6.Hard
Recognise the series and find its sum: S = Σk=1∞ (−1)k+1·0.5ᵏ/k.
ak = (−1)k+1·0.5ᵏ/k
S =
Answer key
- 1. n = 14
- 2. n = 44
- 3. S = 1.947
- 4. R = 0.2
- 5. c₂ = 0.01563
- 6. S = 0.4055
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