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: 21

Answer

Conditionally Convergent

Work Step by Step

Let us consider $a_n=\dfrac{1}{n+3}$ Here, $f(n)=\dfrac{1}{n+3} \implies f'(n)=\dfrac{-1}{(n+3)^2}\lt 0$ The negative sign shows that, the sequence $u_n$ is decreasing. Then, $\lim\limits_{n \to \infty} a_n=\lim\limits_{n \to \infty} \dfrac{1}{n+3}=0$ So, the series converges by the Alternating Test Series. As we can see that $\Sigma_{n=1}^\infty \dfrac{1}{ n}$ diverges by the limit comparison test. Therefore, the series do not converge absolutely this implies that the series is conditionally convergent.
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