The arithmetic sequence 15, 16.5, 18, 19.5, … ends with the term 45. How many terms n does it have?
Sequences & series worksheet with answers
1.Easy
a₁ = 15d = 1.5aₙ = 45
n =
2.Easy
The geometric sequence aₙ = 8·0.75ⁿ⁻¹ decreases. Find the first index n for which aₙ < 0.2.
a₁ = 8r = 0.75ε = 0.2
n =
3.Medium
Apply the ratio test to Σk=1∞ kᵏ/(5ᵏ·k!). Find L = lim |ak+1/ak|.
ak = kᵏ/(5ᵏ·k!)
L =
4.Medium
Apply the ratio test to Σk=1∞ k·5ᵏ/2ᵏ. Find L = lim |ak+1/ak|.
ak = k·5ᵏ/2ᵏ
L =
5.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 1 × 10⁻⁵.
f(x) = eˣx = 2M = 8ε = 1 × 10⁻⁵
n =
6.Hard
Use the Maclaurin polynomial of degree 3 of f(x) = 1/(1 − x) to approximate f(0.5). Give P₃(0.5).
f(x) = 1/(1 − x)n = 3x = 0.5
P₃(0.5) =
Answer key
- 1. n = 21
- 2. n = 14
- 3. L = 0.5437
- 4. L = 2.5
- 5. n = 13
- 6. P₃(0.5) = 1.875
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