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 10.3 - The Integral Test - Exercises 10.3 - Page 586: 8

Answer

Divergent

Work Step by Step

Let us consider $f(x)=\dfrac{\ln x^2}{x}$ Here, the function $f(x)$ is positive, continuous and decreasing for $x \geq 3$ Then $\int_3^\infty \dfrac{\ln x^2}{x}dx= \lim\limits_{k \to \infty} \int_3^k \dfrac{\ln x^2}{x}dx= 2\lim\limits_{k \to \infty} [(\ln^2 (x^2))]_3^k$ and $ \lim\limits_{k \to \infty} [2(\ln^2 (k^2))-2(\ln^2 (3^2))]= \infty$ Thus, the sequence $\Sigma_{n=2}^\infty \dfrac{\ln n^2}{n}=(\dfrac{1}{2}) (\ln 4)+\Sigma_{n=3}^\infty \dfrac{\ln n^2}{n}$ is Divergent.
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