The geometric sequence aₙ = 10·0.8ⁿ⁻¹ decreases. Find the first index n for which aₙ < 0.5.
Sequences & series worksheet with answers
1.Easy
a₁ = 10r = 0.8ε = 0.5
n =
2.Easy
Find the sum S of the infinite series Σk=2∞ 24·(−1/3)ᵏ.
a = 24r = −1/3k₀ = 2
S =
3.Medium
Find the sum S = Σk=1∞ 4/(k(k + 4)).
ak = 4/(k(k + 4))
S =
4.Medium
Exactly one of the four series converges. Click it.
A: Σ (−1)ᵏ/kB: Σ (1 + 1/k)ᵏC: Σ (k + 3)/k²D: Σ (3/2)ᵏ
- 1A: Σ (−1)ᵏ/k
- 2B: Σ (1 + 1/k)ᵏ
- 3C: Σ (k + 3)/k²
- 4D: Σ (3/2)ᵏ
5.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 =
6.Hard
Use the Maclaurin polynomial of degree 5 of f(x) = sin x to approximate f(2). Give P₅(2).
f(x) = sin xn = 5x = 2
P₅(2) =
Answer key
- 1. n = 15
- 2. S = 2
- 3. S = 2.083
- 4. A: Σ (−1)ᵏ/k
- 5. S = 0.2231
- 6. P₅(2) = 0.9333
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