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 522: 25

Answer

$$\ln \left| {x + 1} \right| + \ln \left| {x - 3} \right| + \frac{2}{{x - 3}} + C$$

Work Step by Step

$$\eqalign{ & \int {\frac{{2{x^2} - 10x + 4}}{{\left( {x + 1} \right){{\left( {x - 3} \right)}^2}}}} dx \cr & {\text{The partial fraction decomposition of the integrand is}} \cr & \frac{{2{x^2} - 10x + 4}}{{\left( {x + 1} \right){{\left( {x - 3} \right)}^2}}} = \frac{A}{{x + 1}} + \frac{B}{{x - 3}} + \frac{C}{{{{\left( {x - 3} \right)}^2}}} \cr & {\text{Multiplying by }}\left( {x + 1} \right){\left( {x - 3} \right)^2}{\text{ yields}} \cr & 2{x^2} - 10x + 4 = A{\left( {x - 3} \right)^2} + B\left( {x + 1} \right)\left( {x - 3} \right) + C\left( {x + 1} \right) \cr & 2{x^2} - 10x + 4 = A\left( {{x^2} - 6x + 9} \right) + B\left( {{x^2} - 2x - 3} \right) + Cx + C \cr & 2{x^2} - 10x + 4 = A{x^2} - 6Ax + 9A + B{x^2} - 2Bx - 3B + Cx + C \cr & {\text{Collecting like powers of }}x{\text{}} \cr & 2{x^2} - 10x + 4 = \left( {A{x^2} + B{x^2}} \right) + \left( { - 6Ax - 2Bx + Cx} \right) + \left( {9A - 3B + C} \right) \cr & {\text{Equating corresponding coefficients yields the following system }} \cr & {\text{of linear equations}} \cr & \,\,\,\,\,A + B = 2 \cr & - 6A - 2B + C = - 10 \cr & \,\,\,\,\,9A - 3B + C = 4 \cr & {\text{Solving the system of linear equations we obtain}} \cr & \,\,\,A = 1,\,\,\,B = 1,\,\,\,C = - 2 \cr & \cr & {\text{Then}}{\text{, the integrand can be written as}} \cr & \,\,\frac{{2{x^2} - 10x + 4}}{{\left( {x + 1} \right){{\left( {x - 3} \right)}^2}}} = \frac{1}{{x + 1}} + \frac{1}{{x - 3}} - \frac{2}{{{{\left( {x - 3} \right)}^2}}} \cr & \int {\frac{{2{x^2} - 10x + 4}}{{\left( {x + 1} \right){{\left( {x - 3} \right)}^2}}}} dx = \int {\left[ {\frac{1}{{x + 1}} + \frac{1}{{x - 3}} - \frac{2}{{{{\left( {x - 3} \right)}^2}}}} \right]} dx \cr & {\text{Integrating}} \cr & = \ln \left| {x + 1} \right| + \ln \left| {x - 3} \right| + \frac{2}{{x - 3}} + C \cr} $$
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