Calculus: Early Transcendentals (2nd Edition)

Published by Pearson
ISBN 10: 0321947347
ISBN 13: 978-0-32194-734-5

Chapter 7 - Integration Techniques - Review Exercises - Page 593: 23

Answer

$$2\ln \left| x \right| + 3{\tan ^{ - 1}}\left( {x + 1} \right) + C$$

Work Step by Step

$$\eqalign{ & \int {\frac{{2{x^2} + 7x + 4}}{{{x^3} + 2{x^2} + 2x}}} dx \cr & = \int {\frac{{2{x^2} + 7x + 4}}{{x\left( {{x^2} + 2x + 2} \right)}}} dx \cr & {\text{partial fractions}} \cr & \frac{{2{x^2} + 7x + 4}}{{x\left( {{x^2} + 2x + 2} \right)}} = \frac{A}{x} + \frac{{Bx + C}}{{{x^2} + 2x + 2}} \cr & {\text{multiplying}} \cr & 2{x^2} + 7x + 4 = A\left( {{x^2} + 2x + 2} \right) + \left( {Bx + C} \right)x \cr & 2{x^2} + 7x + 4 = A{x^2} + 2Ax + 2A + B{x^2} + Cx \cr & 2{x^2} + 7x + 4 = \left( {A{x^2} + B{x^2}} \right) + \left( {2Ax + Cx} \right) + 2A \cr & {\text{by equating the coefficients}} \cr & {x^2}:{\text{ }}A + B = 2 \cr & x:{\text{ }}2A + C = 7 \cr & {x^0}:{\text{ }}2A = 4 \cr & {\text{Solving these equations}} \cr & A = 2 \cr & B = 0 \cr & C = 3 \cr & {\text{substituting constants}} \cr & \frac{A}{x} + \frac{{Bx + C}}{{{x^2} + 2x + 2}} = \frac{2}{x} + \frac{3}{{{x^2} + 2x + 2}} \cr & \int {\frac{{2{x^2} + 7x + 4}}{{{x^3} + 2{x^2} + 2x}}} dx = \int {\left( {\frac{2}{x} + \frac{3}{{{x^2} + 2x + 2}}} \right)dx} \cr & = \int {\frac{2}{x}dx} + \int {\frac{3}{{{x^2} + 2x + 2}}dx} \cr & = \int {\frac{2}{x}dx} + \int {\frac{3}{{{x^2} + 2x + 1 + 1}}dx} \cr & = \int {\frac{2}{x}dx} + \int {\frac{3}{{{{\left( {x + 1} \right)}^2} + 1}}dx} \cr & {\text{integrating}} \cr & = 2\ln \left| x \right| + 3{\tan ^{ - 1}}\left( {x + 1} \right) + C \cr} $$
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