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: 50

Answer

The interval of convergence for the series is: $(\dfrac{-13}{2}, \dfrac{19}{2})$, and the radius of convergence is $R=8$.

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{(2x-3^{k+1}}{4^{2k+2}} \times \dfrac{4^{2k}}{(2x-3)^k}|\\=\dfrac{|2x-3|}{16}$ So, we can conclude that the given series converges absolutely if $\dfrac{|2x-3|}{16} \lt 1 \implies \dfrac{-13}{2} \lt x \lt \dfrac{19}{2}$ and diverges if $\dfrac{|2x-3|}{16} \gt 1$ Therefore, the interval of convergence for the series is: $(\dfrac{-13}{2}, \dfrac{19}{2})$, and the radius of convergence is $R=8$.
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