The geometric sequence aₙ = 10·0.6ⁿ⁻¹ decreases. Find the first index n for which aₙ < 0.5.
Sequences & series worksheet with answers
1.Easy
a₁ = 10r = 0.6ε = 0.5
n =
2.Easy
Find the sum S7 of the first 7 terms of the geometric sequence 10, 20, 40, …
a₁ = 10r = 2n = 7
S7 =
3.Medium
Exactly one of the four series converges. Click it.
A: Σ 1/(2ᵏ + k)B: Σ 1/(5k + 5)C: Σ (7/4)ᵏD: Σ ln k / k
- 1A: Σ 1/(2ᵏ + k)
- 2B: Σ 1/(5k + 5)
- 3C: Σ (7/4)ᵏ
- 4D: Σ ln k / k
4.Medium
The power series Σk=1∞ k²·5ᵏ·(x − 2)ᵏ converges on an interval around x₀ = 2. Find the left end x of that interval.
Σ k²·5ᵏ·(x − 2)ᵏx₀ = 2
x =
5.Hard
f(x) = sin 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 0.001.
f(x) = sin xx = 1.5M = 1ε = 0.001
n =
6.Hard
f(x) = eˣ is approximated by its Maclaurin polynomial of degree 5 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 |R₅|.
f(x) = eˣn = 5x = 0.3M = 1.35
|R₅| =
Answer key
- 1. n = 7
- 2. S7 = 1270
- 3. A: Σ 1/(2ᵏ + k)
- 4. x = 1.8
- 5. n = 7
- 6. |R₅| = 1.367 × 10⁻⁶
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