Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 8: Techniques of Integration - Section 8.2 - Integration by Parts - Exercises 8.2 - Page 455: 29

Answer

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

Work Step by Step

$$\eqalign{ & \int {\sin \left( {\ln x} \right)} dx \cr & {\text{Using integration by parts method }} \cr & \,\,\,\,\,{\text{Let }}u = \sin \left( {\ln x} \right),\,\,\,\,du = \frac{{\cos \left( {\ln x} \right)}}{x}dx,\,\,\,\,dv = dx,\,\,\,\,v = x \cr & {\text{Integration by parts then gives}} \cr & = x\sin \left( {\ln x} \right) - \int {x\left( {\frac{{\cos \left( {\ln x} \right)}}{x}} \right)dx} \cr & = x\sin \left( {\ln x} \right) - \int {\cos \left( {\ln x} \right)dx} \cr & \cr & {\text{Integrate by parts again}} \cr & \,\,\,\,\,{\text{Let }}u = \cos \left( {\ln x} \right)dx,\,\,\,\,du = - \frac{{\sin \left( {\ln x} \right)}}{x}dx,\,\,\,\,dv = dx,\,\,\,\,v = x \cr & = x\sin \left( {\ln x} \right) - \left( {x\cos \ln \left( x \right) - \int {x\left( { - \frac{{\sin \left( {\ln x} \right)}}{x}} \right)} dx} \right) \cr & \int {\sin \left( {\ln x} \right)} dx = x\sin \left( {\ln x} \right) - x\cos \ln \left( x \right) - \int {\sin \left( {\ln x} \right)} dx \cr & {\text{combine like integrals and add a constant of integration}} \cr & 2\int {\sin \left( {\ln x} \right)} dx = x\sin \left( {\ln x} \right) - x\cos \ln \left( x \right) + C \cr & {\text{Divide both sides by 2}} \cr & \int {\sin \left( {\ln x} \right)} dx = \frac{1}{2}x\sin \left( {\ln x} \right) - \frac{1}{2}x\cos \ln \left( x \right) + C \cr} $$
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