Calculus (3rd Edition)

Published by W. H. Freeman
ISBN 10: 1464125260
ISBN 13: 978-1-46412-526-3

Chapter 8 - Techniques of Integration - 8.7 Improper Integrals - Exercises - Page 441: 43

Answer

the integral does not converge

Work Step by Step

$\frac{1}{x(2x+5)}$ = $\frac{A}{x}+\frac{B}{2x+5}$ $1$ = $A(2x+5)+Bx$ $A$ = $\frac{1}{5}$ $B$ = $-\frac{2}{5}$ $\int{\frac{dx}{x(2x+5)}}$ = $\frac{1}{5}\int{\frac{dx}{x}}$ - $\frac{2}{5}\int{\frac{dx}{2x+5}}$ = $\frac{1}{5}\ln|x|-\frac{1}{5}\ln|2x+5|+C$ = $\frac{1}{5}\ln|\frac{x}{2x+5}|+C$ $\int_R^1{\frac{dx}{x(2x+5)}}$ = $\frac{1}{5}\ln|\frac{x}{2x+5}| |_R^1$ = $\frac{1}{5}\ln{\frac{1}{7}}-\frac{1}{5}\ln|\frac{R}{2R+5}|$ $I$ = $\lim\limits_{R \to {0^{+}}}$$(\frac{1}{5}\ln{\frac{1}{7}}-\frac{1}{5}\ln|\frac{R}{2R+5}|)$ = $\infty$
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