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: 57

Answer

$$ \int \ln \left(x^{2}-x+2\right) d x = \left(x-\frac{1}{2}\right) \ln \left(x^{2}-x+2\right)-2 x+\sqrt{7} \tan ^{-1} \frac{2 x-1}{\sqrt{7}}+C $$ where $C$ be an arbitrary constant.

Work Step by Step

$$ \int \ln \left(x^{2}-x+2\right) d x $$ $$ \text { Let } u=\ln \left( x^{2}-x+2\right), \quad\quad d v=d x .\\ \text { Then } d u=\frac{2 x-1}{x^{2}-x+2} d x, v=x, $$ and (by integration by parts) , we have : \begin{aligned} \int \ln \left(x^{2}-x+2\right) d x &=x \ln \left(x^{2}-x+2\right)-\int \frac{2 x^{2}-x}{x^{2}-x+2} d x \\ & =x \ln \left(x^{2}-x+2\right)-\int\left(2+\frac{x-4}{x^{2}-x+2}\right) d x \\ &=x \ln \left(x^{2}-x+2\right)-2 x-\int \frac{\frac{1}{2}(2 x-1)}{x^{2}-x+2} d x + \\ & \quad\quad \quad\quad +\frac{7}{2} \int \frac{d x}{\left(x-\frac{1}{2}\right)^{2}+\frac{7}{4}} \\ &=x \ln \left(x^{2}-x+2\right)-2 x-\frac{1}{2} \ln \left(x^{2}-x+2\right)+ \\ & \quad\quad \quad\quad +\frac{7}{2} \int \frac{\frac{\sqrt{7}}{2} d u} {\frac{7}{4}\left(u^{2}+1\right)} \\ &\quad\quad \quad\quad \quad\quad \quad\left[\begin{array}{c} \text { where } x-\frac{1}{2}=\frac{\sqrt{7}}{2} u, \\ d x=\frac{\sqrt{7}}{2} d u, \\ \left(x-\frac{1}{2}\right)^{2}+\frac{7}{4}=\frac{7}{4}\left(u^{2}+1\right) \end{array}\right] \\ &=\left(x-\frac{1}{2}\right) \ln \left(x^{2}-x+2\right)-2 x+\sqrt{7} \tan ^{-1} u+C \\ &=\left(x-\frac{1}{2}\right) \ln \left(x^{2}-x+2\right)-2 x+\sqrt{7} \tan ^{-1} \frac{2 x-1}{\sqrt{7}}+C \end{aligned} So the integral: $$ \int \ln \left(x^{2}-x+2\right) d x = \left(x-\frac{1}{2}\right) \ln \left(x^{2}-x+2\right)-2 x+\sqrt{7} \tan ^{-1} \frac{2 x-1}{\sqrt{7}}+C $$ where $C$ be an arbitrary constant.
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.