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 10.1 - Sequences - Exercises 10.1 - Page 571: 121

Answer

$\{a_{n}\}$ is convergent.

Work Step by Step

$a_{n}=\displaystyle \frac{1}{\sqrt{n}}+\sqrt{2}\geq\sqrt{2}$ $\{a_{n}\}$ is bounded below by $\sqrt{2}$ $\displaystyle \frac{1}{\sqrt{n}}$ is the greatest when n is the smallest (n=1) $\{a_{n}\} $ is bounded above by $\sqrt{2}+1$ $\{a_{n}\}$ is bounded. If we can show that it is monotonic, we can apply Th. 6. \begin{align*} \sqrt{n+1}&\geq\sqrt{n} \\ \sqrt{n+1}+\sqrt{2n(n+1)}&\geq\sqrt{n} +\sqrt{2n(n+1)}\\ \displaystyle \frac{\sqrt{n+1}+\sqrt{2n(n+1)}}{\sqrt{n(n+1)}}&\displaystyle \geq\frac{\sqrt{n} +\sqrt{2n(n+1)}}{\sqrt{n(n+1)}} \\ \displaystyle \frac{1}{\sqrt{n}}+\sqrt{2}&\geq \displaystyle \frac{1}{\sqrt{n}+1}+\sqrt{2}\\ a_{n}&\geq a_{n+1} \\ \end{align*} $\{a_{n}\}$ is nonincreasing, that is, monotonic. Th.6 applies. $\{a_{n}\}$ is convergent.
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