Answer
$\frac{1}{2}(\cos 8x+\cos 2x)$
Work Step by Step
Use the third Sum-to-Product Formula on page 559, $\cos u\cos v=\frac{1}{2}[\cos(u+v)+\cos(u-v)]$
$\cos 5x\cos 3x$
$=\frac{1}{2}[\cos(5x+3x)+\cos(5x-3x)]$
$=\frac{1}{2}(\cos 8x+\cos 2x)$
Precalculus: Mathematics for Calculus, 7th Edition
by Stewart, James; Redlin, Lothar; Watson, Saleem
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
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