The arithmetic sequence 15, 18, 21, 24, … ends with the term 120. How many terms n does it have?
Sequences & series worksheet with answers
1.Easy
a₁ = 15d = 3aₙ = 120
n =
2.Easy
Find the sum S38 of the first 38 terms of the arithmetic sequence 17, 15, 13, 11, …
a₁ = 17d = −2n = 38
S38 =
3.Medium
Exactly one of the four series converges. Click it.
A: Σ (3/2)ᵏB: Σ (−1)ᵏ/kC: Σ k!/10ᵏD: Σ ln k / k
- 1A: Σ (3/2)ᵏ
- 2B: Σ (−1)ᵏ/k
- 3C: Σ k!/10ᵏ
- 4D: Σ ln k / k
4.Medium
Apply the ratio test to Σk=1∞ (k!)²·3ᵏ/(2k)!. Find L = lim |ak+1/ak|.
ak = (k!)²·3ᵏ/(2k)!
L =
5.Hard
f(x) = eˣ is approximated at x = 0.5 by its Maclaurin polynomial of degree n. With the Lagrange bound M·|x|ⁿ⁺¹/(n + 1)! and M = 2, find the smallest degree n that guarantees an error below 0.0005.
f(x) = eˣx = 0.5M = 2ε = 0.0005
n =
6.Hard
Use the Maclaurin polynomial of degree 4 of f(x) = 1/(1 − x) to approximate f(0.5). Give P₄(0.5).
f(x) = 1/(1 − x)n = 4x = 0.5
P₄(0.5) =
Answer key
- 1. n = 36
- 2. S38 = −760
- 3. B: Σ (−1)ᵏ/k
- 4. L = 0.75
- 5. n = 5
- 6. P₄(0.5) = 1.938
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