The geometric sequence aₙ = 20·0.6ⁿ⁻¹ decreases. Find the first index n for which aₙ < 0.1.
Sequences & series worksheet with answers
1.Easy
a₁ = 20r = 0.6ε = 0.1
n =
2.Easy
Find the sum S6 of the first 6 terms of the geometric sequence 4, −12, 36, …
a₁ = 4r = −3n = 6
S6 =
3.Medium
Apply the ratio test to Σk=1∞ kᵏ/(3ᵏ·k!). Find L = lim |ak+1/ak|.
ak = kᵏ/(3ᵏ·k!)
L =
4.Medium
Find the radius of convergence R of the power series Σk=1∞ k!·xᵏ/kᵏ.
Σ k!·xᵏ/kᵏx₀ = 0
R =
5.Hard
Use the Maclaurin polynomial of degree 3 of f(x) = ln(1 + 2x) to approximate f(0.25). Give P₃(0.25).
f(x) = ln(1 + 2x)n = 3x = 0.25
P₃(0.25) =
6.Hard
f(x) = eˣ is approximated at x = 2 by its Maclaurin polynomial of degree n. With the Lagrange bound M·|x|ⁿ⁺¹/(n + 1)! and M = 8, find the smallest degree n that guarantees an error below 1 × 10⁻⁵.
f(x) = eˣx = 2M = 8ε = 1 × 10⁻⁵
n =
Answer key
- 1. n = 12
- 2. S6 = −728
- 3. L = 0.9061
- 4. R = 2.718
- 5. P₃(0.25) = 0.4167
- 6. n = 13
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