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: 16

Answer

$\displaystyle \frac{1}{2}+\ln 6$

Work Step by Step

$\displaystyle \frac{x^{3}+4x^{2}+x-1}{x^{3}+x^{2}}=\frac{(x^{3}+x^{2})+3x^{2}+x-1}{x^{3}+x^{2}}=1+\frac{3x^{2}+x-1}{x^{3}+x^{2}}$ $=1+\displaystyle \frac{3x^{2}+x-1}{x^{2}(x+1)}$ repeated factor $=1 +\displaystyle \frac{A}{x}+\frac{B}{x^{2}}+\frac{C}{x+1}$ $3x^{2}+x-1=Ax(x+1)+B(x+1)+Cx^{2}$ $3x^{2}+x-1=Ax^{2}+Ax+Bx+B+Cx^{2}$ $3x^{2}+x-1=(A+C)x^{2}+(A+B)x+B\Rightarrow\left[\begin{array}{lll} B=-1 & & \\ A+B=1 & \Rightarrow A=2 & \\ A+C=3 & & \Rightarrow C=1 \end{array}\right]$ $\displaystyle \int_{1}^{2}\frac{x^{3}+4x^{2}+x-1}{x^{3}+x^{2}}dx=\int_{1}^{2}(1 +\frac{2}{x}-\frac{1}{x^{2}}+\frac{1}{x+1})dx$ $=\left[x+2\ln|x|+\dfrac{1}{x}+\ln|x+1|\right]_{1}^{2}$ $=(2+2\displaystyle \ln 2+\frac{1}{2}+\ln 3)-(1+0+1+\ln 2)$ $=\displaystyle \frac{1}{2}+\ln 2+\ln 3$ $=\displaystyle \frac{1}{2}+\ln 6$
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