Find the sum S of the infinite series Σk=1∞ 4·(2/5)ᵏ.
Sequences & series worksheet with answers
1.Easy
a = 4r = 2/5k₀ = 1
S =
2.Easy
Find the sum S27 of the first 27 terms of the arithmetic sequence −4, −6, −8, −10, …
a₁ = −4d = −2n = 27
S27 =
3.Medium
Apply the ratio test to Σk=1∞ k²·3ᵏ/4ᵏ. Find L = lim |ak+1/ak|.
ak = k²·3ᵏ/4ᵏ
L =
4.Medium
Apply the ratio test to Σk=1∞ 3ᵏ·k!/kᵏ. Find L = lim |ak+1/ak|.
ak = 3ᵏ·k!/kᵏ
L =
5.Hard
Recognise the series and find its sum: S = Σk=1∞ k·(1/3)ᵏ.
ak = k·(1/3)ᵏ
S =
6.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 1 × 10⁻⁶.
f(x) = eˣx = 0.5M = 2ε = 1 × 10⁻⁶
n =
Answer key
- 1. S = 2.667
- 2. S27 = −810
- 3. L = 0.75
- 4. L = 1.104
- 5. S = 0.75
- 6. n = 7
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