Find the sum S21 of the first 21 terms of the arithmetic sequence −3, 0, 3, 6, …
Sequences & series worksheet with answers
1.Easy
a₁ = −3d = 3n = 21
S21 =
2.Easy
The geometric sequence aₙ = 3·0.75ⁿ⁻¹ decreases. Find the first index n for which aₙ < 0.1.
a₁ = 3r = 0.75ε = 0.1
n =
3.Medium
Find the sum S = Σk=1∞ 2/(k(k + 1)).
ak = 2/(k(k + 1))
S =
4.Medium
Exactly one of the four series converges. Click it.
A: Σ (2/5)ᵏB: Σ (3k + 1)/(k + 2)C: Σ (4/3)ᵏD: Σ 1/k
- 1A: Σ (2/5)ᵏ
- 2B: Σ (3k + 1)/(k + 2)
- 3C: Σ (4/3)ᵏ
- 4D: Σ 1/k
5.Hard
f(x) = eˣ is approximated by its Maclaurin polynomial of degree 5 at x = −0.5. Use the Lagrange error bound M·|x|ⁿ⁺¹/(n + 1)! with M = 1 to find the largest possible error |R₅|.
f(x) = eˣn = 5x = −0.5M = 1
|R₅| =
6.Hard
Use the Maclaurin polynomial of degree 2 of f(x) = e2x to approximate f(0.8). Give P₂(0.8).
f(x) = e2xn = 2x = 0.8
P₂(0.8) =
Answer key
- 1. S21 = 567
- 2. n = 13
- 3. S = 2
- 4. A: Σ (2/5)ᵏ
- 5. |R₅| = 2.17 × 10⁻⁵
- 6. P₂(0.8) = 3.88
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