University Calculus: Early Transcendentals (3rd Edition)

Published by Pearson
ISBN 10: 0321999584
ISBN 13: 978-0-32199-958-0

Chapter 9 - Section 9.6 - Alternating Series and Conditional Convergence - Exercises - Page 521: 30

Answer

Converges conditionally

Work Step by Step

The Alternating Series Test states: Consider a series $\Sigma a_n$ such that $A_n=(-1)^n B_n$; $B_n \geq 0$ for all $n$ If the following conditions are satisfied, then the series converges: a) $\lim\limits_{n \to \infty} B_n=0$; b) $B_n$ is a decreasing sequence. We notice that $B_n=\dfrac{\ln n}{n- \ln n}$ a) $\lim\limits_{n \to \infty} p_n=\lim\limits_{n \to \infty}\dfrac{\ln n}{n- \ln n}=\dfrac{\frac{1}{n}}{1-\frac{1}{n}}=0$; b) Now, $B_n=\dfrac{\ln n}{n- \ln n}$ we can notice from a decreasing sequence that $B'_n=\dfrac{1-\ln n}{(n- \ln n)^2}\lt 0$ Therefore, the given series converges conditionally by the Alternating Series Test.
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