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: 28

Answer

$$2\ln \left| {x + 1} \right| + \frac{1}{{x + 1}} - \frac{1}{{{{\left( {x + 1} \right)}^2}}} + C$$

Work Step by Step

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