The geometric sequence aₙ = 2·0.7ⁿ⁻¹ decreases. Find the first index n for which aₙ < 0.1.
Sequences & series worksheet with answers
1.Easy
a₁ = 2r = 0.7ε = 0.1
n =
2.Easy
The geometric sequence aₙ = 8·0.8ⁿ⁻¹ decreases. Find the first index n for which aₙ < 0.01.
a₁ = 8r = 0.8ε = 0.01
n =
3.Medium
Apply the ratio test to Σk=1∞ (k!)²·1ᵏ/(2k)!. Find L = lim |ak+1/ak|.
ak = (k!)²·1ᵏ/(2k)!
L =
4.Medium
Find the sum S = Σk=1∞ 5/(k(k + 3)).
ak = 5/(k(k + 3))
S =
5.Hard
Use the Maclaurin polynomial of degree 3 of f(x) = 1/(1 − 2x) to approximate f(−0.2). Give P₃(−0.2).
f(x) = 1/(1 − 2x)n = 3x = −0.2
P₃(−0.2) =
6.Hard
Recognise the series and find its sum: S = Σk=1∞ (−1)k+1·0.2ᵏ/k.
ak = (−1)k+1·0.2ᵏ/k
S =
Answer key
- 1. n = 10
- 2. n = 31
- 3. L = 0.25
- 4. S = 3.056
- 5. P₃(−0.2) = 0.696
- 6. S = 0.1823
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