The geometric sequence aₙ = 2·0.85ⁿ⁻¹ decreases. Find the first index n for which aₙ < 0.01.
Sequences & series worksheet with answers
1.Easy
a₁ = 2r = 0.85ε = 0.01
n =
2.Easy
Find the sum S20 of the first 20 terms of the arithmetic sequence −8, −2, 4, 10, …
a₁ = −8d = 6n = 20
S20 =
3.Medium
Find the radius of convergence R of the power series Σk=1∞ k!·xᵏ/kᵏ.
Σ k!·xᵏ/kᵏx₀ = 0
R =
4.Medium
Find the sum S = Σk=1∞ 5/(k(k + 4)).
ak = 5/(k(k + 4))
S =
5.Hard
Recognise the series and find its sum: S = Σk=0∞ (−1)ᵏ·22k/(2k)!.
ak = (−1)ᵏ·22k/(2k)!
S =
6.Hard
f(x) = cos x is approximated at x = 1.5 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 0.0005.
f(x) = cos xx = 1.5M = 1ε = 0.0005
n =
Answer key
- 1. n = 34
- 2. S20 = 980
- 3. R = 2.718
- 4. S = 2.604
- 5. S = −0.4161
- 6. n = 8
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