The geometric sequence aₙ = 2·0.9ⁿ⁻¹ decreases. Find the first index n for which aₙ < 0.5.
Sequences & series worksheet with answers
1.Easy
a₁ = 2r = 0.9ε = 0.5
n =
2.Easy
Find the sum S of the infinite series Σk=1∞ 18·(1/2)ᵏ.
a = 18r = 1/2k₀ = 1
S =
3.Medium
Exactly one of the four series diverges. Click it.
A: Σ 1/k³B: Σ (−1)ᵏ/√kC: Σ (5k + 1)/(k + 2)D: Σ (1/2)ᵏ
- 1A: Σ 1/k³
- 2B: Σ (−1)ᵏ/√k
- 3C: Σ (5k + 1)/(k + 2)
- 4D: Σ (1/2)ᵏ
4.Medium
Find the radius of convergence R of the power series Σk=1∞ 5ᵏ·xᵏ/(k + 1).
Σ 5ᵏ·xᵏ/(k + 1)x₀ = 0
R =
5.Hard
Find the coefficient c₂ of (x − 4)² in the Taylor series of f(x) = √x about a = 4.
f(x) = √xa = 4k = 2
c₂ =
6.Hard
Recognise the series and find its sum: S = Σk=0∞ 1.5ᵏ/k!.
ak = 1.5ᵏ/k!
S =
Answer key
- 1. n = 15
- 2. S = 18
- 3. C: Σ (5k + 1)/(k + 2)
- 4. R = 0.2
- 5. c₂ = −0.01563
- 6. S = 4.482
Full step-by-step solutions: practise this topic on examproblems.com.