Calculus, 10th Edition (Anton)

Published by Wiley
ISBN 10: 0-47064-772-8
ISBN 13: 978-0-47064-772-1

Chapter 7 - Principles Of Integral Evaluation - 7.5 Integrating Rational Functions By Partial Fractions - Exercises Set 7.5 - Page 521: 18

Answer

$$x + 4\ln \left| {x - 2} \right| - \ln \left| {x - 1} \right| + C$$

Work Step by Step

$$\eqalign{ & \int {\frac{{{x^2}}}{{{x^2} - 3x + 2}}} dx \cr & {\text{The integrand is an improper rational function since the numerator }} \cr & {\text{has degree 2 and the denominator 2}}{\text{. Thus}}{\text{, using the long division}} \cr & \,\,\,\,\,\,\frac{{{x^2}}}{{{x^2} - 3x + 2}} = 1 + \frac{{3x - 2}}{{{x^2} - 3x + 2}} \cr & {\text{The integrand can be expressed as}} \cr & \int {\left( {1 + \frac{{3x - 2}}{{{x^2} - 3x + 2}}} \right)} dx \cr & = x + \int {\frac{{3x - 2}}{{{x^2} - 3x + 2}}} dx \cr & {\text{Decomposing the integrand into partial fractions}} \cr & {\text{Factor the denominator}} \cr & \frac{{3x - 2}}{{{x^2} - 3x + 2}} = \frac{{3x - 2}}{{\left( {x - 2} \right)\left( {x - 1} \right)}} \cr & \frac{{3x - 2}}{{\left( {x - 2} \right)\left( {x - 1} \right)}} = \frac{A}{{x - 2}} + \frac{B}{{x - 1}} \cr & {\text{Multiplying the equation by }}\left( {x - 2} \right)\left( {x - 1} \right){\text{, we have}} \cr & 3x - 2 = A\left( {x - 1} \right) + B\left( {x - 2} \right) \cr & {\text{if we set }}x = 2 \cr & 3\left( 2 \right) - 2 = A\left( {2 - 1} \right) + B\left( 0 \right) \cr & A = 4 \cr & {\text{if we set }}x = 1 \cr & 3\left( 1 \right) - 2 = A\left( {x - 1} \right) + B\left( {x - 2} \right) \cr & 1 = A\left( 0 \right) + B\left( {1 - 2} \right) \cr & B = - 1 \cr & \cr & {\text{then}} \cr & x + \int {\frac{{3x - 2}}{{{x^2} - 3x + 2}}} dx = x + \int {\left( {\frac{4}{{x - 2}} - \frac{1}{{x - 1}}} \right)} dx \cr & {\text{Integrating}} \cr & = x + 4\ln \left| {x - 2} \right| - \ln \left| {x - 1} \right| + C \cr} $$
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