Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 8: Techniques of Integration - Section 8.8 - Improper Integrals - Exercises 8.8 - Page 501: 55

Answer

Diverges

Work Step by Step

Use a direct limit comparison test. Since, $\cos x \geq -1$ This implies that $\dfrac{1}{x} \leq \dfrac{2 +\cos x}{x}$ for all $x \geq \pi$ Now, $\lim\limits_{a \to \infty}\int_{\pi}^{a} \dfrac{dx}{x}=\lim\limits_{a \to \infty}[\ln|x|]_{\pi}^{a}\\\lim\limits_{a \to \infty}\ln|a| -\lim\limits_{a \to \infty}\ln| \pi| \\ =\infty$ Thus, the given integral diverges by the direct comparison test.
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