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 8.3 - Trigonometric Integrals - Exercises 8.3 - Page 463: 52

Answer

$$\frac{1}{2}\cos x - \frac{1}{{10}}\cos 5x + C $$

Work Step by Step

$$\eqalign{ & \int {\sin 2x} \cos 3xdx \cr & {\text{Use the identity }}\sin mx\cos nx = \frac{1}{2}\left[ {\sin \left( {m - n} \right)x + \sin \left( {m + n} \right)x} \right]\,\,\left( {{\text{see page 463}}} \right) \cr & \int {\sin 3x} \cos 2xdx = \int {\frac{1}{2}} \left[ {\sin \left( {2 - 3} \right)x + \sin \left( {2 + 3} \right)x} \right]dx \cr & = \int {\frac{1}{2}} \left( {\sin \left( { - x} \right) + \sin 5x} \right)dx \cr & = \frac{1}{2}\int {\left( { - \sin x + \sin 5x} \right)} dx \cr & {\text{distribute}} \cr & = - \frac{1}{2}\int {\sin x} dx + \frac{1}{2}\int {\sin 5x} dx \cr & {\text{integrating}} \cr & = - \frac{1}{2}\left( { - \cos x} \right) + \frac{1}{2}\left( { - \frac{1}{5}\cos 5x} \right) + C \cr & = \frac{1}{2}\cos x - \frac{1}{{10}}\cos 5x + C \cr} $$
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