Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 11 - Infinite Sequences and Series - 11.4 The Comparison Tests - 11.4 Exercises - Page 772: 42

Answer

\[\sum_{n=1}^{\infty}a_n=\sum_{n=1}^{\infty}\frac{1}{n^2}\] and \[\sum_{n=1}^{\infty}b_n=\sum_{n=1}^{\infty}\frac{1}{n}\]

Work Step by Step

Let \[\sum_{n=1}^{\infty}a_n=\sum_{n=1}^{\infty}\frac{1}{n^2}\] and \[\sum_{n=1}^{\infty}b_n=\sum_{n=1}^{\infty}\frac{1}{n}\] \[\Rightarrow a_n=\frac{1}{n^2},\;\;\;b_n=\frac{1}{n}\] \[\Rightarrow \frac{a_n}{b_n}=\frac{\frac{1}{n^2}}{\frac{1}{n}}=\frac{1}{n}\] \[\Rightarrow \lim_{n\rightarrow \infty}\frac{a_n}{b_n}=\lim_{n\rightarrow\infty}\frac{1}{n}=0\] [P-Series Test: $\displaystyle\sum_{n=1}^{\infty}\frac{1}{n^P}$ is convergent if and only if P>1] $\displaystyle\Rightarrow \sum_{n=1}^{\infty}b_n=\sum_{n=1}^{\infty}\frac{1}{n}$ is divergent by P-Series Test and $\displaystyle\sum_{n=1}^{\infty}a_n=\sum_{n=1}^{\infty}\frac{1}{n^2}$ is convergent by P-Series Test.
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