The geometric sequence aₙ = 5·0.9ⁿ⁻¹ decreases. Find the first index n for which aₙ < 0.2.
Sequences & series worksheet with answers
1.Easy
a₁ = 5r = 0.9ε = 0.2
n =
2.Easy
The arithmetic sequence 14, 14.5, 15, 15.5, … ends with the term 25.5. How many terms n does it have?
a₁ = 14d = 0.5aₙ = 25.5
n =
3.Medium
Exactly one of the four series diverges. Click it.
A: Σ 1/(k² + 7)B: Σ k²/3ᵏC: Σ 2ᵏ/k³D: Σ (1/2)ᵏ
- 1A: Σ 1/(k² + 7)
- 2B: Σ k²/3ᵏ
- 3C: Σ 2ᵏ/k³
- 4D: Σ (1/2)ᵏ
4.Medium
Find the sum S = Σk=1∞ 4/(k(k + 2)).
ak = 4/(k(k + 2))
S =
5.Hard
f(x) = cos x is approximated at x = 2 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) = cos xx = 2M = 1ε = 0.001
n =
6.Hard
f(x) = eˣ is approximated at x = 2 by its Maclaurin polynomial of degree n. With the Lagrange bound M·|x|ⁿ⁺¹/(n + 1)! and M = 8, find the smallest degree n that guarantees an error below 0.0005.
f(x) = eˣx = 2M = 8ε = 0.0005
n =
Answer key
- 1. n = 32
- 2. n = 24
- 3. C: Σ 2ᵏ/k³
- 4. S = 3
- 5. n = 9
- 6. n = 10
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