Calculus: Early Transcendentals 9th Edition

Published by Cengage Learning
ISBN 10: 1337613924
ISBN 13: 978-1-33761-392-7

Chapter 7 - Section 7.8 - Improper Integrals - 7.8 Exercises - Page 550: 61

Answer

Divergent

Work Step by Step

Define $f(x)=\frac{x+1}{\sqrt{x^4-x}}$ and $g(x)=\frac{1}{x}+\frac{1}{x^2}$. For $x\geq 1$, $-x<0$ $x^4-x\frac{x+1}{x^2}$ $f(x)>g(x)$ Find the convergence for $\int_1^\infty g(x) dx$: $\int_1^\infty \frac{1}{x}+\frac{1}{x^2} dx=[\ln x-\frac{1}{x}]_1^\infty=(\ln \infty -\frac{1}{\infty})-(\ln 1-\frac{1}{1}=(\infty -0)-(0-1)=\infty (\text{divergent})$ Since $f(x)>g(x)$ for $x\geq 1$ and $\int_1^\infty g(x)$ is divergent, using the Comparison Theorem it concludes that $\int_1^\infty \frac{x+1}{\sqrt{x^4-x}}dx$ is divergent.
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