The geometric sequence aₙ = 20·0.6ⁿ⁻¹ decreases. Find the first index n for which aₙ < 0.05.
Sequences & series worksheet with answers
1.Easy
a₁ = 20r = 0.6ε = 0.05
n =
2.Easy
Find the sum S7 of the first 7 terms of the geometric sequence 5, 15, 45, …
a₁ = 5r = 3n = 7
S7 =
3.Medium
Apply the ratio test to Σk=1∞ k!/kᵏ. Find L = lim |ak+1/ak|.
ak = k!/kᵏ
L =
4.Medium
Find the radius of convergence R of the power series Σk=1∞ (2k)!·(x − 3)ᵏ/(k!)².
Σ (2k)!·(x − 3)ᵏ/(k!)²x₀ = 3
R =
5.Hard
f(x) = eˣ is approximated by its Maclaurin polynomial of degree 3 at x = 0.3. Use the Lagrange error bound M·|x|ⁿ⁺¹/(n + 1)! with M = e0.3 = 1.35 to find the largest possible error |R₃|.
f(x) = eˣn = 3x = 0.3M = 1.35
|R₃| =
6.Hard
f(x) = ln(1 + x) is approximated by its Maclaurin polynomial of degree 2 at x = 0.1. Use the Lagrange error bound M·|x|ⁿ⁺¹/(n + 1)! with M = 2! = 2 to find the largest possible error |R₂|.
f(x) = ln(1 + x)n = 2x = 0.1M = 2
|R₂| =
Answer key
- 1. n = 13
- 2. S7 = 5465
- 3. L = 0.3679
- 4. R = 0.25
- 5. |R₃| = 0.0004556
- 6. |R₂| = 0.0003333
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