Calculus, 10th Edition (Anton)

Published by Wiley
ISBN 10: 0-47064-772-8
ISBN 13: 978-0-47064-772-1

Chapter 9 - Infinite Series - 9.3 Infinite Series - Exercises Set 9.3 - Page 621: 7

Answer

convergent $S=\dfrac{1}{3}$

Work Step by Step

Given $$ \sum_{k=1}^{\infty} \frac{1}{(k+2)(k+3)}$$ Since by using partial fractions $$\frac{1}{(k+2)(k+3)}=\frac{1}{(k+2) }-\frac{1}{ (k+3)} $$ Then \begin{align*} \lim _{n \rightarrow \infty} \sum_{k=1}^{n} \frac{1}{k+2}-\frac{1}{k+3}& =\lim _{n \rightarrow \infty}\bigg\{\left[\frac{1}{1+2}-\frac{1}{Y+3}\right] +\left[\frac{1}{2+2}-\frac{1}{2+3}\right]\\ &\ \ \ \ +\left[\frac{1}{3+2}-\frac{1}{3+3}\right]+\cdots +\left[\frac{1}{n+2}-\frac{1}{n+3}\right]\bigg\}\\ &=\lim _{n \rightarrow \infty}\left(\frac{1}{3}-\frac{1}{n+3}\right)\\ &=\frac{1}{3} \end{align*} Hence the series is convergent and has sum $\frac{1}{3}$
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