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: 20

Answer

$-\displaystyle \ln 2-\frac{1}{2}-\frac{\ln 5}{3}$

Work Step by Step

$\displaystyle \frac{3x-5x^{2}}{(x-1)^{2}(3x-1)}=\frac{A}{3x-1}+\frac{B}{x-1}+\frac{C}{(x-1)^{2}}$ $\displaystyle \frac{(-5x^{2}+3x)(x-1)^{2}(3x-1)}{(x-1)^{2}(3x-1)}=\frac{A(x-1)^{2}(3x-1)}{3x-1}+\frac{B(x-1)^{2}(3x-1)}{x-1}+\frac{C(x-1)^{2}(3x-1)}{(x-1)^{2}}$ $3x-5x^{2}=A(x-1)^{2}+B(3x-1)(x-1)+C(3x-1)$ $3x-5x^{2}=A(x^{2}-2x+1)+B(3x^{2}-4x+1)+3Cx-C$ $-5x^{2}+3x+0=x^{2}(A+3B)+x(-2A-4B+3C)+(A+B-C)$ $\left\{\begin{array}{lllll} A & +3B & & =-5 & \\ -2A & -4B & +3C & =3 & /+2R_{1}\\ A & +B & -C & =0 & /-R_{1} \end{array}\right.$ $\left\{\begin{array}{lllll} A & +3B & & =-5 & \\ & 2B & +3C & =-7 & /\\ & -2B & -C & =5 & /+R_{2} \end{array}\right.$ $\left\{\begin{array}{llllll} A & +3B & & =-5 & & \\ & 2B & +3C & =-7 & / & \\ & & 2C & =-2 & \Rightarrow & C=-1 \end{array}\right.$ Eq 2 $\Rightarrow B=-2$ Eq 1 $\Rightarrow A=1$ $\displaystyle \frac{x(3-5x)}{(3x-1)(x-1)^{2}}=\frac{1}{3x-1}-\frac{2}{x-1}-\frac{1}{(x-1)^{2}}$ $\displaystyle \int_{2}^{3}\frac{x(3-5x)}{(3x-1)(x-1)^{2}}dx= \left|\frac{1}{3}\ln|3x-1|-2\ln|x-1|+\frac{1}{x-1}\right|_{2}^{3}$ $=\displaystyle \frac{1}{3}\ln 8-2\ln 2+\frac{1}{2}-(\frac{1}{3}\ln 5-0+1)$ $=\displaystyle \frac{1}{3}\cdot 3\ln 2-2\ln 2+\frac{1}{2}-\frac{1}{3}\ln 5-1$ $=-\displaystyle \ln 2-\frac{1}{2}-\frac{\ln 5}{3}$
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