Multivariable Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 0-53849-787-4
ISBN 13: 978-0-53849-787-9

Chapter 11 - Infinite Sequences and Series - 11.1 Exercises - Page 725: 74

Answer

{$a_{n}$} is a bounded sequence.

Work Step by Step

$a_{n} = \frac{2n-3}{3n+4}$ $f(x)= \frac{2x-3}{3x+4}$ $f'(x)= \frac{(3x+4)(2)-(2x-3)(3)}{(3x+4)^{2}}$ $=\frac{6x+8-6x+9}{(3x+4)^{2}}$ $=\frac{17}{(3x+4)^{2}} \gt 0$ for all $x$ Thus $f$ is an increasing function So $a_{n} \lt a_{n+1}$ and the sequence is an increasing sequence. $a_{1}=\frac{-1}{7}$, $a_{2}=\frac{1}{10}$, $a_{3}=\frac{3}{13}$, ... Thus $a_{n} \geq -\frac{1}{7}$ for all $n \geq 1$ And so {$a_{n}$} is bounded below by $-\frac{1}{17}$ $\lim\limits_{n \to \infty}a_{n} = \lim\limits_{n \to \infty} \frac{2n-3}{3n+4}$ $=\lim\limits_{n \to \infty} \frac{2-\frac{3}{n}}{3+\frac{4}{n}}=\frac{2}{3}$ The sequence {$a_{n}$} is bounded above by $\frac{2}{3}$ Therefore {$a_{n}$} is a bounded sequence.
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