Calculus: Early Transcendentals 9th Edition

Published by Cengage Learning
ISBN 10: 1337613924
ISBN 13: 978-1-33761-392-7

Chapter 7 - Section 7.4 - Integration of Rational Functions by Partial Fractions. - 7.4 Exercises - Page 515: 25

Answer

$\frac{5}{2} - \ln \left( 6 \right)$

Work Step by Step

$$\eqalign{ & \int_{ - 1}^0 {\frac{{{x^3} - 4x + 1}}{{{x^2} - 3x + 2}}} dx \cr & {\text{The degree of the numerator is greater than the degree of the }} \cr & {\text{denominator}},{\text{ we first perform the long division}} \cr & \frac{{{x^3} - 4x + 1}}{{{x^2} - 3x + 2}} = x + 3 + \frac{{3x - 5}}{{{x^2} - 3x + 2}} \cr & {\text{The partial fraction decomposition of }}\frac{{3x - 5}}{{{x^2} - 3x + 2}}{\text{ has the}} \cr & {\text{form}} \cr & \frac{{3x - 5}}{{{x^2} - 3x + 2}} = \frac{{3x - 5}}{{\left( {x - 2} \right)\left( {x - 1} \right)}} = \frac{A}{{x - 2}} + \frac{B}{{x - 1}} \cr & {\text{Multiply both sides by the least common denominator}} \cr & 3x - 5 = A\left( {x - 1} \right) + B\left( {x - 2} \right) \cr & x = 2 \to A = 1 \cr & x = 1 \to B = 2 \cr & \frac{{3x - 5}}{{\left( {x - 2} \right)\left( {x - 1} \right)}} = \frac{1}{{x - 2}} + \frac{2}{{x - 1}} \cr & {\text{Therefore}} \cr & \frac{{{x^3} - 4x + 1}}{{{x^2} - 3x + 2}} = x + 3 + \frac{1}{{x - 2}} + \frac{2}{{x - 1}} \cr & \int_{ - 1}^0 {\frac{{{x^3} - 4x + 1}}{{{x^2} - 3x + 2}}} dx = \int_{ - 1}^0 {\left( {x + 3 + \frac{1}{{x - 2}} + \frac{2}{{x - 1}}} \right)} dx \cr & {\text{Intergating}} \cr & = \left[ {\frac{1}{2}{x^2} + 3x + \ln \left| {x - 2} \right| + 2\ln \left| {x - 1} \right|} \right]_{ - 1}^0 \cr & {\text{Evaluating}} \cr & = \left[ {\frac{1}{2}{{\left( 0 \right)}^2} + 3\left( 0 \right) + \ln \left| {0 - 2} \right| + 2\ln \left| {0 - 1} \right|} \right] \cr & - \left[ {\frac{1}{2}{{\left( { - 1} \right)}^2} + 3\left( { - 1} \right) + \ln \left| { - 1 - 2} \right| + 2\ln \left| { - 1 - 1} \right|} \right] \cr & {\text{Simplifying}} \cr & = \ln 2 - \left( { - \frac{5}{2} + \ln 3 + 2\ln 2} \right) \cr & = \ln 2 + \frac{5}{2} - \ln 3 - 2\ln 2 \cr & = \frac{5}{2} - \ln 3 - \ln 2 \cr & = \frac{5}{2} - \ln \left( 6 \right) \cr} $$
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