Find the sum S of the infinite series Σk=1∞ 2·(−3/4)ᵏ.
Sequences & series worksheet with answers
1.Easy
a = 2r = −3/4k₀ = 1
S =
2.Easy
Find the term a37 of the arithmetic sequence 12, 14, 16, 18, …
a₁ = 12d = 2n = 37
a37 =
3.Medium
Apply the root test to Σk=1∞ ((1k + 3)/(3k + 3))ᵏ. Find L = lim |ak|1/k.
ak = ((1k + 3)/(3k + 3))ᵏ
L =
4.Medium
Exactly one of the four series converges. Click it.
A: Σ (3/5)ᵏB: Σ (4k + 1)/(k + 2)C: Σ (3/2)ᵏD: Σ ln k / k
- 1A: Σ (3/5)ᵏ
- 2B: Σ (4k + 1)/(k + 2)
- 3C: Σ (3/2)ᵏ
- 4D: Σ ln k / k
5.Hard
f(x) = cos x is approximated at x = 0.5 by its Maclaurin polynomial of degree n. With the Lagrange bound M·|x|ⁿ⁺¹/(n + 1)! and M = 1, find the smallest degree n that guarantees an error below 1 × 10⁻⁶.
f(x) = cos xx = 0.5M = 1ε = 1 × 10⁻⁶
n =
6.Hard
Recognise the series and find its sum: S = Σk=1∞ (−1)k+1·0.25ᵏ/k.
ak = (−1)k+1·0.25ᵏ/k
S =
Answer key
- 1. S = −0.8571
- 2. a37 = 84
- 3. L = 0.3333
- 4. A: Σ (3/5)ᵏ
- 5. n = 7
- 6. S = 0.2231
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