Calculus: Early Transcendentals 8th Edition

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

Chapter 7 - Section 7.5 - Strategy for Integration - 7.5 Exercises - Page 507: 12

Answer

$ -\displaystyle \ln x+\frac{1}{2}\ln(x^{2}+3)+\frac{2}{\sqrt{3}}\tan^{-1}(\frac{x}{\sqrt{3}})+C$

Work Step by Step

Strategy: Rational function. Partial fractions $\displaystyle \frac{2x-3}{x(x^{2}+3)}=\frac{A}{x}+\frac{Bx+C}{x^{2}+3}$ $\displaystyle \frac{2x-3}{x(x^{2}+3)}=\frac{Ax^{2}+3A+Bx^{2}+Cx}{x(x^{2}+3)}$ $2x-3=(A+B)x^{2}+Cx+3A\Rightarrow\left\{\begin{array}{l} A+B=0\\ C=2\\ 3A=-3 \end{array}\right.$ $A=-1, B=1, C=2$ $\displaystyle \int\frac{2x-3}{x(x^{2}+3)}dx=\int-\frac{1}{x}dx+\int\frac{x+2}{x^{2}+3}$ $=-\displaystyle \int\frac{1}{x}dx+\int\frac{xdx}{x^{2}+3}+2\int\frac{dx}{x^{2}+3}=-I_{1}+I_{2}+2I_{3}$ $I_{1}=\ln x+C_{1}$ $I_{2}=\displaystyle \left[\begin{array}{l} t=x^{2}+3\\ dt=2xdx \end{array}\right]=\frac{1}{2}\int\frac{dt}{t}=\frac{1}{2}\ln t=\frac{1}{2}\ln(x^{2}+3)+C_{2}$ $I_{3}=\displaystyle \left[17. \quad \int\frac{dx}{x^{2}+a^{2}}=\frac{1}{a}\tan^{-1}\frac{x}{a}\right]=\frac{1}{\sqrt{3}}\tan^{-1}(\frac{x}{\sqrt{3}})+C_{3}$ $-I_{1}+I_{2}+2I_{3}=-\displaystyle \ln x+\frac{1}{2}\ln(x^{2}+3)+\frac{2}{\sqrt{3}}\tan^{-1}(\frac{x}{\sqrt{3}})+C$
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