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Question

Use the test of your choice to determine whether the following series converge.

k=1(1k+2k)\sum _ { k = 1 } ^ { \infty } \left( \frac { 1 } { k } + 2 ^ { - k } \right)

Solution

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Answered 12 months ago
Answered 12 months ago
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Let ak=1k, bk=2k.a_k=\dfrac {1} {k}, \ b_k=2^{-k}.

Then,

ak\sum a_k

diverges (Harmonic series) and

bk\sum b_k

converges (Geometric series, r=1/2r=1/2).

By Theorem 10.8, Property (4)

(ak+bk) diverges \quad \Rightarrow \quad \sum (a_k+b_k) \quad \text { diverges }

So,

k=1(1k+2k) diverges\sum_{k=1}^{\infty} \left( \frac {1} {k} +2^{-k}\right) \quad \text { diverges}

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