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 10.7 - Power Series - Exercises 10.7 - Page 613: 38

Answer

$\dfrac{9}{4}$

Work Step by Step

Let us apply the Ratio Test to the given series. $\lim\limits_{n \to \infty} |\dfrac{a_{n+1}}{a_n}|=|\lim\limits_{n \to \infty} \dfrac{(2n+2)^2 \cdot x}{(3n+2)^2} | \\=|x| \lim\limits_{n \to \infty}\dfrac{ (2+\dfrac{2}{n})^2 }{3+\dfrac{2}{n}} \\=\dfrac{4}{9}|x|$ So, $\dfrac{4}{9}|x|| \lt 1 $ and $|x| \lt \dfrac{9}{4}$ The radius of convergence is: $\dfrac{9}{4}$
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