Calculus, 10th Edition (Anton)

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

Chapter 9 - Infinite Series - 9.6 Alternating Series; Absolute And Conditional Convergence - Exercises Set 9.6 - Page 646: 7

Answer

Converges absolutely

Work Step by Step

Let ${a_k} = {\left( { - \dfrac{3}{5}} \right)^k} = {\left( { - 1} \right)^k}{\left( {\dfrac{3}{5}} \right)^k}$. Evaluate the limit: $\rho = \mathop {\lim }\limits_{k \to \infty } \dfrac{{\left| {{a_{k + 1}}} \right|}}{{\left| {{a_k}} \right|}} = \mathop {\lim }\limits_{k \to \infty } \dfrac{{{{\left( {\dfrac{3}{5}} \right)}^{k + 1}}}}{{{{\left( {\dfrac{3}{5}} \right)}^k}}} = \mathop {\lim }\limits_{k \to \infty } \dfrac{3}{5} = \dfrac{3}{5}$ The series converges absolutely by the ratio test for absolute convergence because $\rho = \dfrac{3}{5} \lt 1$. Hence, it converges.
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