Find the sum S7 of the first 7 terms of the geometric sequence 4, −12, 36, …
Sequences & series worksheet with answers
1.Easy
a₁ = 4r = −3n = 7
S7 =
2.Easy
Find the sum S of the infinite series Σk=0∞ 6·(−1/4)ᵏ.
a = 6r = −1/4k₀ = 0
S =
3.Medium
The power series Σk=1∞ k²·5ᵏ·(x + 2)ᵏ converges on an interval around x₀ = −2. Find the right end x of that interval.
Σ k²·5ᵏ·(x + 2)ᵏx₀ = −2
x =
4.Medium
Apply the ratio test to Σk=1∞ k²·5ᵏ/3ᵏ. Find L = lim |ak+1/ak|.
ak = k²·5ᵏ/3ᵏ
L =
5.Hard
f(x) = sin x 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 = 1, find the smallest degree n that guarantees an error below 0.0005.
f(x) = sin xx = 0.5M = 1ε = 0.0005
n =
6.Hard
Recognise the series and find its sum: S = Σk=0∞ (−1)ᵏ·22k+1/(2k + 1)!.
ak = (−1)ᵏ·22k+1/(2k + 1)!
S =
Answer key
- 1. S7 = 2188
- 2. S = 4.8
- 3. x = −1.8
- 4. L = 1.667
- 5. n = 4
- 6. S = 0.9093
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