The geometric sequence aₙ = 5·0.75ⁿ⁻¹ decreases. Find the first index n for which aₙ < 0.5.
Sequences & series worksheet with answers
1.Easy
a₁ = 5r = 0.75ε = 0.5
n =
2.Easy
Find the sum S20 of the first 20 terms of the arithmetic sequence 4, 9, 14, 19, …
a₁ = 4d = 5n = 20
S20 =
3.Medium
Exactly one of the four series diverges. Click it.
A: Σ (2/3)ᵏB: Σ k²/2ᵏC: Σ (5/3)ᵏD: Σ 1/(k(k + 1))
- 1A: Σ (2/3)ᵏ
- 2B: Σ k²/2ᵏ
- 3C: Σ (5/3)ᵏ
- 4D: Σ 1/(k(k + 1))
4.Medium
Find the sum S = Σk=1∞ 12/(k(k + 1)).
ak = 12/(k(k + 1))
S =
5.Hard
f(x) = eˣ is approximated at x = 1 by its Maclaurin polynomial of degree n. With the Lagrange bound M·|x|ⁿ⁺¹/(n + 1)! and M = 3, find the smallest degree n that guarantees an error below 0.001.
f(x) = eˣx = 1M = 3ε = 0.001
n =
6.Hard
f(x) = sin x is approximated at x = 1 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 0.0001.
f(x) = sin xx = 1M = 1ε = 0.0001
n =
Answer key
- 1. n = 10
- 2. S20 = 1030
- 3. C: Σ (5/3)ᵏ
- 4. S = 12
- 5. n = 6
- 6. n = 7
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