Calculus: Early Transcendentals 8th Edition

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

Chapter 7 - Section 7.4 - Integration of Rational Functions by Partial Fractions. - 7.4 Exercises - Page 501: 17

Answer

$\displaystyle \frac{27\ln 2-9\ln 3}{5} \approx 1.76549$

Work Step by Step

$\displaystyle \frac{4y^{2}-7y-12}{y(y+2)(y-3)}=\frac{A}{y}+\frac{B}{y+2}+\frac{C}{y-3}$ $4y^{2}-7y-12=A(y+2)(y-3)+By(y-3)+Cy(y+2)$ $4y^{2}-7y-12=A(y^{2}-y-6)+By^{2}-3By+Cy^{2}+2Cy$ $4y^{2}-7y-12=Ay^{2}-Ay-6A+By^{2}-3By+Cy^{2}+2Cy$ $4y^{2}-7y-12=(A+B+C)y^{2}+(-A-3B+2C)y+(-6A)$ $\left\{\begin{array}{llllll} -6A=-12 & \Rightarrow & A & & =2 & \\ -A-3B+2C=-7 & \Rightarrow & -3B & +2C & =-5 & ...I\\ A+B+C=4 & \Rightarrow & B & +C & =2 & ...II \end{array}\right.$ $I+3(II)\displaystyle \Rightarrow 5C=1\Rightarrow C=\frac{1}{5}$ $II\displaystyle \Rightarrow B=2-\frac{1}{5}=\frac{9}{5}$ $\displaystyle \int_{1}^{2}\dfrac{4y^{2}-7y-12}{y(y+2)(y-3)}dy=\int_{1}^{2}(\frac{2}{y}+\frac{\frac{9}{5}}{y+2}+\frac{\frac{1}{5}}{y-3})$ $=\left[2\ln|y|+\dfrac{9}{5}\ln|y+2|+\dfrac{1}{5}\ln|y-3|\right]_{1}^{2}$ $=2\displaystyle \ln 2+\frac{9}{5}\ln 4+0-(0+\frac{9}{5}\ln 3+\frac{1}{5} \ln 2)$ $=2\displaystyle \ln 2+\frac{18}{5}\ln 2-\frac{1}{5}\ln 2-\frac{9}{5} \ln 3$ $=\displaystyle \frac{27}{5} \ln 2- \displaystyle \frac{9}{5}\ln 3$ $=\displaystyle \frac{27\ln 2-9\ln 3}{5} \approx 1.76549$
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