Find the sum S5 of the first 5 terms of the geometric sequence 5, −15, 45, …
Sequences & series worksheet with answers
1.Easy
a₁ = 5r = −3n = 5
S5 =
2.Easy
A ball is dropped and its first rebound reaches 8 m. Every next rebound reaches 75% of the previous one. Which rebound n is the first one lower than 0.01 m?
a₁ = 8r = 0.75ε = 0.01
n =
3.Medium
Apply the ratio test to Σk=1∞ (k!)²·5ᵏ/(2k)!. Find L = lim |ak+1/ak|.
ak = (k!)²·5ᵏ/(2k)!
L =
4.Medium
The power series Σk=1∞ (x − 2)ᵏ/(k·2ᵏ) converges on an interval around x₀ = 2. Find the right end x of that interval.
Σ (x − 2)ᵏ/(k·2ᵏ)x₀ = 2
x =
5.Hard
Find the coefficient c₄ of (x − 1)⁴ in the Taylor series of f(x) = √x about a = 1.
f(x) = √xa = 1k = 4
c₄ =
6.Hard
Recognise the series and find its sum: S = Σk=0∞ 1.5ᵏ/k!.
ak = 1.5ᵏ/k!
S =
Answer key
- 1. S5 = 305
- 2. n = 25
- 3. L = 1.25
- 4. x = 4
- 5. c₄ = −0.03906
- 6. S = 4.482
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