Calculus with Applications (10th Edition)

Published by Pearson
ISBN 10: 0321749006
ISBN 13: 978-0-32174-900-0

Chapter 8 - Further Techniques and Applications of Integration - 8.4 Improper Integrals - 8.4 Exercises - Page 452: 17

Answer

Divergent

Work Step by Step

\[\begin{align} & \int_{-\infty }^{-1}{\ln \left| x \right|}dx \\ & \text{From the definition of absolute value} \\ & \int_{-\infty }^{-1}{\ln \left| x \right|}dx=\int_{1}^{\infty }{\ln x}dx \\ & \text{Then,} \\ & \int_{1}^{\infty }{\ln x}dx=\underset{b\to \infty }{\mathop{\lim }}\,\int_{1}^{b}{\ln x}dx \\ & \text{Integrating} \\ & \text{=}\underset{b\to \infty }{\mathop{\lim }}\,\left[ x\ln x-x \right]_{1}^{b} \\ & \text{=}\underset{b\to \infty }{\mathop{\lim }}\,\left[ \left( b\ln b-b \right)-\left( 1\ln \left( 1 \right)-1 \right) \right] \\ & \text{=}\underset{b\to \infty }{\mathop{\lim }}\,\left[ \left( b(\ln b-1) \right)+1 \right] \\ & \text{Evaluate when }b\to \infty \\ & \text{=}\infty (\ln \infty -1) +1 \\ & =\infty \\ & \text{ The improper integral diverges.} \\ & \text{Divergent} \\ \end{align}\]
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