Calculus (3rd Edition)

Published by W. H. Freeman
ISBN 10: 1464125260
ISBN 13: 978-1-46412-526-3

Chapter 8 - Techniques of Integration - 8.1 Integration by Parts - Exercises - Page 395: 46

Answer

$$\frac{1}{2} x(\sin (\ln x)- \cos (\ln x))+C$$

Work Step by Step

Given$$\int \sin (\ln x)dx $$ Let $$z=\ln x\ \ \ \ \ \ dz=\frac{1}{x}dx $$ Then $$ \int \sin (\ln x)dx =\int e^z\sin zdz $$ \begin{align*} u &= \sin z \ \ \ \ \ \ \ \ \ dv= e^ zdz\\ du &= \cos z dz \ \ \ \ \ \ \ \ v= e^ z \end{align*} Then \begin{align*} \int \sin z e^{ z} d x &=(\sin z)\left(e^{ z}\right)-\int e^{ z} \cos z d z \\ &=e^{ z} \sin z- \int \cos z e^{ z} d z \end{align*} For the integral part again, let \begin{align*} u &= \cos z\ \ \ \ \ \ \ \ \ dv= e^ zdz\\ du &= -\sin zdz \ \ \ \ \ \ \ \ v= e^z \end{align*}Then, \begin{align*} \int \sin z e^{z} d &=e^{z} \sin z-\left(e^{z} \cos z+ \int e^{z} \sin z d z\right)\\ \int \sin ze^{z} dz&=e^{z} \sin z- e^{z} \cos z- \int e^{z} \sin z dz\\ 2 \int \sin z e^{z} d x&=e^{z} \sin z- e^{z} \cos z\\ \int \sin z e^{z} d z&=\frac{1}{2} e^{z}(\sin z- \cos z)+C \end{align*} Hence $$\int \sin (\ln x)dx =\frac{1}{2} x(\sin (\ln x)- \cos (\ln x))+C $$
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.