The geometric sequence aₙ = 3·0.75ⁿ⁻¹ decreases. Find the first index n for which aₙ < 0.05.
Sequences & series worksheet with answers
1.Easy
a₁ = 3r = 0.75ε = 0.05
n =
2.Easy
Find the sum S7 of the first 7 terms of the geometric sequence 2, −6, 18, …
a₁ = 2r = −3n = 7
S7 =
3.Medium
Find the radius of convergence R of the power series Σk=1∞ (x + 1)ᵏ/(k·4ᵏ).
Σ (x + 1)ᵏ/(k·4ᵏ)x₀ = −1
R =
4.Medium
The power series Σk=1∞ k!·(x + 1)ᵏ/kᵏ converges on an interval around x₀ = −1. Find the left end x of that interval.
Σ k!·(x + 1)ᵏ/kᵏx₀ = −1
x =
5.Hard
Use the Maclaurin polynomial of degree 4 of f(x) = 1/(1 − x) to approximate f(0.5). Give P₄(0.5).
f(x) = 1/(1 − x)n = 4x = 0.5
P₄(0.5) =
6.Hard
f(x) = sin x is approximated by its Maclaurin polynomial of degree 2 at x = −0.5. Use the Lagrange error bound M·|x|ⁿ⁺¹/(n + 1)! with M = 1 to find the largest possible error |R₂|.
f(x) = sin xn = 2x = −0.5M = 1
|R₂| =
Answer key
- 1. n = 16
- 2. S7 = 1094
- 3. R = 4
- 4. x = −3.718
- 5. P₄(0.5) = 1.938
- 6. |R₂| = 0.02083
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