Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 7 - Section 7.3 - Double-Angle, Half-Angle, and Product-Sum Formulas - 7.3 Exercises - Page 561: 58


$\frac{1}{2}(\cos 8x+\cos 2x)$

Work Step by Step

Use the third Sum-to-Product Formula on page 559, $\cos u\cos v=\frac{1}{2}[\cos(u+v)+\cos(u-v)]$ $\cos 5x\cos 3x$ $=\frac{1}{2}[\cos(5x+3x)+\cos(5x-3x)]$ $=\frac{1}{2}(\cos 8x+\cos 2x)$
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