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Q. 13

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Calculus
Found in: Page 631
Calculus

Calculus

Book edition 1st
Author(s) Peter Kohn, Laura Taalman
Pages 1155 pages
ISBN 9781429241861

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Short Answer

Let 0 < p < 1. Evaluate the limit limk1/k lnk1/kp

Explain why we cannot use a p-series with 0 < p < 1 in a limit comparison test to verify the divergence of the series k=21k log k

The p-series is divergent for 0<p<1. The limit comparison test if the ratio is zero states that if limkakbkand k=1bk converges, then k=1ak convergesThe limit comparison test fails to give any information about the divergence of the series k=21k lnk

See the step by step solution

Step by Step Solution

Step 1. Given

k=21k log k

Step 2.Finding the value of the expression

The value of the expression is limk1/k lnk1/kplimk1/k lnk1/kp=limkkpk ln k=limkkp-1ln k=limk(p-1)kp-21k(using's l hospital rule)=limk(p-1)k1-p=0

Step 3. Limit comparison test

The limit comparison test states that for and be two series with positive terms then If limkakbk=L Where L is any positive real number then either both converges or diverges.If limkakbk=0 and k=1 bk converges then k=1 ak converges.If limkakbk= and k=1 bk diverges then k=1 ak diverges.

Step 4. Result

The value of the expression is limk1/k lnk1/kp=0The p-series is divergent for 0<p<1. The limit comparison test if the ratio is zero states that if limkakbkand k=1bk converges, then k=1ak convergesThe limit comparison test fails to give any information about the divergence of the series k=21k lnk

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