Calculus: Early Transcendentals 9th Edition

Published by Cengage Learning
ISBN 10: 1337613924
ISBN 13: 978-1-33761-392-7

Chapter 11 - Section 11.4 - The Comparison Tests - 11.4 Exercises - Page 765: 33

Answer

Converges

Work Step by Step

We use the Limit Comparison Test with $a_n=(1+\frac{1}{n})^2e^{-n}$ and $b_n=e^{-n}$ and obtain $\lim\limits_{n \to \infty}\frac{a_n}{b_n}=\lim\limits_{n \to \infty}\frac{(1+\frac{1}{n})^2e^{-n}}{e^{-n}}=\lim\limits_{n \to \infty}(1+\frac{1}{n})^2=(1+0)^2=1>0$. Notice that $\sum_{n=1}^\infty e^{-n}=\sum_{n=1}^\infty (\frac{1}{e})^n$ is a geometric series with the common ratio $1/e$.
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