Calculus: Early Transcendentals 8th Edition

Published by Cengage Learning
ISBN 10: 1285741552
ISBN 13: 978-1-28574-155-0

Chapter 7 - Section 7.8 - Improper Integrals - 7.8 Exercises - Page 535: 53

Answer

Diverges

Work Step by Step

$\displaystyle \int_0^1\frac{\sec^2x}{x\sqrt{x}}\ dx = \int_0^1\frac{dx}{x\sqrt{x} \cos^2x}$ Find a lesser-valued function: $\displaystyle \frac{1}{x\sqrt{x} \cos^2x} > \frac{1}{2x\sqrt{x} } = \frac{x^{-\frac{3}{2}}}{2}$ (Recall: $\displaystyle 0 \le \cos x \le 1$, so substitute with 2 as this will make the value lower since it is in denominator) $\displaystyle \frac{1}{2}\int_0^1x^{-\frac{3}{2}}\ dx = \lim\limits_{t \to 0} \frac{1}{2} \int_t^1x^{-\frac{3}{2}}\ dx$ $\displaystyle = \frac{1}{2}\lim\limits_{t \to 0} \left[ -2x^{-\frac{1}{2}} \right]_t^1$ $\displaystyle = -\lim\limits_{t \to 0} \left[ 1-\frac{1}{\sqrt{t}}) \right]$ $\displaystyle = - \left[ 1-\infty \right]$ Divergent by the comparison theorem, since the lesser-valued function diverges.
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