Calculus 10th Edition

Published by Brooks Cole
ISBN 10: 1-28505-709-0
ISBN 13: 978-1-28505-709-5

Chapter 9 - Inifnite Series - 9.1 Exercises - Page 592: 26

Answer

$\displaystyle \lim_{n\rightarrow\infty}a_{n}=0$ (please see step-by-step)

Work Step by Step

Our inference, based on the graph (see below) is that the sequence converges to 0. Analytically, we use Th.9.1: [ Let $L$ be a real number. Let $f$ be a function of a real variable such that $\displaystyle \lim_{x\rightarrow\infty}f(x)=L$. If $\{a_{n}\}$ is a sequence such that $f(n)=a_{n}$ for every positive integer $n$, then $\displaystyle \lim_{n\rightarrow\infty}a_{n}=L$. ] We define $f(x)=\displaystyle \frac{1}{x^{3/2}}$, for which $a_{n}=f(n)$ . As $ x\rightarrow\infty$, the numerator becomes very large, and $f(x)\rightarrow 0.$ So, $\displaystyle \lim_{n\rightarrow\infty}a_{n}=\lim_{n\rightarrow\infty}\frac{1}{n^{3/2}}=\lim_{x\rightarrow\infty}\frac{1}{x^{3/2}}=0$.
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