Calculus, 10th Edition (Anton)

Published by Wiley
ISBN 10: 0-47064-772-8
ISBN 13: 978-0-47064-772-1

Chapter 9 - Infinite Series - 9.8 Maclaurin And Taylor Series; Power Series - Exercises Set 9.8 - Page 667: 48

Answer

The given series converges only at $x=2$, and the radius of convergence is $R=0$.

Work Step by Step

Ratio Test: Let us consider a series $\Sigma a_k$ whose limit $l$ can be obtained as: $ l=\lim\limits_{k \to \infty} |\dfrac{a_{k+1}}{a_k}|$ 1. For $l \lt 1$, the series is absolutely convergent. 2. For $l \gt 1$, the series is divergent. 3. For $l = 1$, the series is inconclusive. Therefore, $ L=\lim\limits_{k \to \infty} |\dfrac{a_{k+1}}{a_k}|\\=\lim\limits_{k \to \infty} |\dfrac{(2k+3)!}{(k+1)^3}(x-2)^{k+1} \times \dfrac{k^3}{(2k+1)!(x-2)^k}| \\=\lim\limits_{k \to \infty}|x-2| \dfrac{(2k+3)(2k+2)k^3}{(k+1)^3}\\=+ \infty$ So, we can conclude that the given series converges only at $x=2$, and the radius of convergence is $R=0$.
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