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: 15

Answer

$\displaystyle \frac{5}{2}-\ln 6$

Work Step by Step

$x(x^{2}-3x+2)=x^{3}-3x^{2}+2x$ $\displaystyle \frac{x^{3}-4x+1}{x^{2}-3x+2}=\frac{x(x^{2}-3x+2)+3x^{2}-6x+1}{x^{2}-3x+2}$ $=x+\displaystyle \frac{3x^{2}-6x+1}{x^{2}-3x+2}=x+\frac{3(x^{2}-3x+2) +3x-5}{x^{2}-3x+2}$ $=x+3+\displaystyle \frac{3x-5}{x^{2}-3x+2}$ the denominator can be factored, $=x+3+\displaystyle \frac{3x-5}{(x-2)(x-1)}$ $\displaystyle \frac{3x-5}{(x-2)(x-1)}=\frac{A}{x-2}+\frac{B}{x-1}$ $\displaystyle \frac{3x-5}{(x-2)(x-1)}=\frac{(A+B)x+(-A-2B)}{(x-2)(x-1)}$ $\left\{\begin{array}{llll} A & +B & =3 & ...I\\ -A & -2B & =-5 & ...II \end{array}\right.$ Adding the two equations $\Rightarrow B=2, A=1$ $\displaystyle \int_{-1}^{0}\frac{x^{3}-4x+1}{x^{2}-3x+2}dx=\int(x+3+\frac{1}{x-2}+\frac{2}{x-1})dx$ $= \left[\frac{x^{2}}{2}+3x+\ln|x-2|+2\ln|x-1|\right]_{-1}^{0}$ $=(\displaystyle \ln 2)-(\frac{1}{2}-3+\ln 3+2\ln 2)$ $=\displaystyle \frac{5}{2}-\ln 2-\ln 3$ $=\displaystyle \frac{5}{2}-(\ln 2+\ln 3)$ $=\displaystyle \frac{5}{2}-\ln 6$
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