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Conditional and absolute convergence: For each of the series that follow, determine whether the series converges absolutely, converges conditionally, or diverges. Explain the criteria you are using and why your conclusion is valid.

k=1(-1)ke-k

Short Answer

Expert verified

The series k=1(-1)ke-k converges absolutely.

Step by step solution

01

Step 1. Given Information.

The series:

k=1(-1)ke-k

02

Step 2. By Alternating Series Test.

According to the Alternating Series Test, the sequence ak+1<akfor every . Then the alternating series ak+1,akboth converges.

03

Step 3. Find ak+1.

ak=e-kak+1=e-(k+1)=e-k-1ak+1<ak

So the sequence is monotonic decreasing sequence.

04

Step 4. Find limk→∞ak.

limkak=limke-k=0

So the series converges.

05

Step 5. Find ak+1ak.

limkak+1ak=limk(-1)k+1e-k-1(-1)ke-k=limk1eL=1e<1

So the series converges absolutely.

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