Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 8: Techniques of Integration - Section 8.5 - Integration of Rational Functions by Partial Fractions - Exercises 8.5 - Page 476: 35

Answer

$$9x + 2\ln \left| x \right| + \frac{1}{x} + 7\ln \left| {x - 1} \right| + C$$

Work Step by Step

$$\eqalign{ & \int {\frac{{9{x^3} - 3x + 1}}{{{x^3} - {x^2}}}} dx \cr & \cr & {\text{Apply long division to the integrand}} \cr & \frac{{9{x^3} - 3x + 1}}{{{x^3} - {x^2}}} = 9 + \frac{{9{x^2} - 3x + 1}}{{{x^3} - {x^2}}} \cr & {\text{Then}}{\text{,}} \cr & \int {\frac{{9{x^3} - 3x + 1}}{{{x^3} - {x^2}}}} dx = \int {\left( {9 + \frac{{9{x^2} - 3x + 1}}{{{x^3} - {x^2}}}} \right)} dx \cr & = \int 9 dx + \int {\frac{{9{x^2} - 3x + 1}}{{{x^3} - {x^2}}}} dx \cr & = 9x + \int {\frac{{9{x^2} - 3x + 1}}{{{x^3} - {x^2}}}} dx \cr & \cr & {\text{Solve the integral by the method of partial fractions.}} \cr & {\text{The form of the partial fraction decomposition is}} \cr & \frac{{9{x^2} - 3x + 1}}{{{x^3} - {x^2}}} = \frac{{9{x^2} - 3x + 1}}{{{x^2}\left( {x - 1} \right)}} = \frac{A}{x} + \frac{B}{{{x^2}}} + \frac{C}{{x - 1}} \cr & {\text{Multiplying by }}{x^2}\left( {x - 1} \right){\text{, we have}} \cr & 9{x^2} - 3x + 1 = Ax\left( {x - 1} \right) + B\left( {x - 1} \right) + C{x^2} \cr & \cr & {\text{if we set }}x = 0, \cr & 1 = A\left( 0 \right) + B\left( { - 1} \right) + C\left( 0 \right) \cr & B = - 1 \cr & {\text{if we set }}x = 1 \cr & 7 = A\left( 0 \right) + B\left( 0 \right) + C{\left( 1 \right)^2} \cr & C = 7 \cr & {\text{if we set }}x = 2,\,\,B = - 1{\text{ and }}C = 7 \cr & 9{\left( 2 \right)^2} - 3\left( 2 \right) + 1 = A\left( 2 \right)\left( {2 - 1} \right) + \left( { - 1} \right)\left( {2 - 1} \right) + \left( 7 \right){\left( 2 \right)^2} \cr & 31 = 2A - 1 + 28 \cr & A = 2 \cr & \frac{{9{x^2} - 3x + 1}}{{{x^2}\left( {x - 1} \right)}} = \frac{2}{x} - \frac{1}{{{x^2}}} + \frac{7}{{x - 1}} \cr & \int {\frac{{9{x^2} - 3x + 1}}{{{x^3} - {x^2}}}} dx = \int {\left( {\frac{2}{x} - \frac{1}{{{x^2}}} + \frac{7}{{x - 1}}} \right)} dx \cr & = 2\ln \left| x \right| + \frac{1}{x} + 7\ln \left| {x - 1} \right| + C \cr & {\text{Then}}{\text{,}} \cr & 9x + \int {\frac{{9{x^2} - 3x + 1}}{{{x^3} - {x^2}}}} dx = 9x + 2\ln \left| x \right| + \frac{1}{x} + 7\ln \left| {x - 1} \right| + C \cr} $$
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