Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 10: Infinite Sequences and Series - Section 10.6 - Alternating Series and Conditional Convergence - Exercises 10.6 - Page 603: 25

Answer

Converges Conditionally

Work Step by Step

Let us consider $a_n=(-1)^{n+1}\dfrac{1+n}{n^2}$ we can see that $\Sigma_{n=1}^\infty |a_n|=\Sigma_{n=1}^\infty \dfrac{1+n}{n^2}=\Sigma_{n=1}^\infty \dfrac{1}{n^2}+\Sigma_{n=1}^\infty \dfrac{1}{n}$ Here,we can see that the series $\Sigma_{n=1}^\infty \dfrac{1}{n^2}$ shows a convergent p-series and the series $\Sigma_{n=1}^\infty \dfrac{1}{n}$ shows a divergent p-series. This implies that the sum of both the series defines divergent. Need to consider $b_n=\dfrac{1}{n^2}+\dfrac{1}{n}$ we can see that $b_n$ is increasing and $\lim\limits_{n \to \infty} b_n=\lim\limits_{n \to \infty} (\dfrac{1}{n^2})+\lim\limits_{n \to \infty} (\dfrac{1}{n})=0$ Therefore, the series Converges Conditionally by the Alternating Series Test.
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