Find the sum S of the infinite series Σk=1∞ 9·(−2/5)ᵏ.
Sequences & series worksheet with answers
1.Easy
a = 9r = −2/5k₀ = 1
S =
2.Easy
The arithmetic sequence 4, 6, 8, 10, … ends with the term 50. How many terms n does it have?
a₁ = 4d = 2aₙ = 50
n =
3.Medium
Exactly one of the four series converges. Click it.
A: Σ 1/(4k + 3)B: Σ (1 + 1/k)ᵏC: Σ ln k / kD: Σ 1/(3ᵏ + k)
- 1A: Σ 1/(4k + 3)
- 2B: Σ (1 + 1/k)ᵏ
- 3C: Σ ln k / k
- 4D: Σ 1/(3ᵏ + k)
4.Medium
Exactly one of the four series diverges. Click it.
A: Σ k³/3ᵏB: Σ 5/k³C: Σ k!/3ᵏD: Σ (−1)ᵏ/√k
- 1A: Σ k³/3ᵏ
- 2B: Σ 5/k³
- 3C: Σ k!/3ᵏ
- 4D: Σ (−1)ᵏ/√k
5.Hard
Recognise the series and find its sum: S = Σk=0∞ (−1)ᵏ·1.52k+1/(2k + 1)!.
ak = (−1)ᵏ·1.52k+1/(2k + 1)!
S =
6.Hard
f(x) = eˣ is approximated at x = 1 by its Maclaurin polynomial of degree n. With the Lagrange bound M·|x|ⁿ⁺¹/(n + 1)! and M = 3, find the smallest degree n that guarantees an error below 1 × 10⁻⁵.
f(x) = eˣx = 1M = 3ε = 1 × 10⁻⁵
n =
Answer key
- 1. S = −2.571
- 2. n = 24
- 3. D: Σ 1/(3ᵏ + k)
- 4. C: Σ k!/3ᵏ
- 5. S = 0.9975
- 6. n = 8
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