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Give an example of convergent series ∑k=1∞akand ∑k=1∞bksuch that the series ∑k=1∞akbkdiverges.

Short Answer

Expert verified

∑k=1∞akbk=∑k=1∞1kdiverges

Step by step solution

01

Step 1. Given information

∑k=1∞akand∑k=1∞bkconverges

02

Step 2. Check if ∑k=1∞akand ∑k=1∞bk converges

∑k=1∞ (−1)k+1akand ∑k=1∞ (−1)kakboth converge

Therefore,

∑k=1∞ ak=(−1)kkconverges

Now,

∑k=1∞ bk=(−1)kkdiverges

03

Step 3. Check if ∑k=1∞ak bk diverges

∑k=1∞ akbk=∑k=1∞ (−1)kk⋅(−1)kk=∑k=1∞ 1k

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