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: 48

Answer

$$\frac{1}{5}\ln \left| {4x - 1} \right| - \frac{1}{{10}}\ln \left( {4{x^2} + 1} \right) - \frac{1}{{10}}{\tan ^{ - 1}}2x + C$$

Work Step by Step

$$\eqalign{ & \int {\frac{{dx}}{{16{x^3} - 4{x^2} + 4x - 1}}} \cr & {\text{Decompose the integrand into partial fractions}} \cr & \frac{1}{{16{x^3} - 4{x^2} + 4x - 1}} = \frac{1}{{\left( {4x - 1} \right)\left( {4{x^2} + 1} \right)}} \cr & \frac{1}{{\left( {4x - 1} \right)\left( {4{x^2} + 1} \right)}} = \frac{A}{{4x - 1}} + \frac{{Bx + C}}{{4{x^2} + 1}} \cr & 1 = A\left( {4{x^2} + 1} \right) + \left( {Bx + C} \right)\left( {4x - 1} \right) \cr & 1 = 4A{x^2} + A + 4B{x^2} - Bx + 4Cx - C \cr & {\text{Collect like terms}} \cr & 1 = \left( {4A{x^2} + 4B{x^2}} \right) + \left( { - Bx + 4Cx} \right) + A - C \cr & 4A + 4B = 0,{\text{ }} - B + 4C = 0,{\text{ }}A - C = 1 \cr & {\text{Solving we obtain}} \cr & A = \frac{4}{5},{\text{ }}B = - \frac{4}{5},{\text{ }}C = - \frac{1}{5} \cr & \frac{1}{{\left( {4x - 1} \right)\left( {4{x^2} + 1} \right)}} = \frac{4}{{5\left( {4x - 1} \right)}} - \frac{{4x + 1}}{{5\left( {4{x^2} + 1} \right)}} \cr & \int {\frac{{dx}}{{16{x^3} - 4{x^2} + 4x - 1}}} = \int {\frac{4}{{5\left( {4x - 1} \right)}}dx} - \int {\frac{{4x + 1}}{{5\left( {4{x^2} + 1} \right)}}} dx \cr & = \frac{1}{5}\int {\frac{4}{{4x - 1}}dx} - \frac{1}{5}\int {\frac{{4x}}{{4{x^2} + 1}}} dx - \frac{1}{5}\int {\frac{1}{{4{x^2} + 1}}} dx \cr & = \frac{1}{5}\int {\frac{4}{{4x - 1}}dx} - \frac{1}{{10}}\int {\frac{{8x}}{{4{x^2} + 1}}} dx - \frac{1}{{10}}\int {\frac{2}{{4{x^2} + 1}}} dx \cr & {\text{Integrating}} \cr & = \frac{1}{5}\ln \left| {4x - 1} \right| - \frac{1}{{10}}\ln \left( {4{x^2} + 1} \right) - \frac{1}{{10}}{\tan ^{ - 1}}2x + C \cr} $$
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