Answer
$ 5[\cos{2x} - \cos{8x}]$
Work Step by Step
$\sin{A} \sin{B} = \dfrac{1}{2} [\cos{(A-B)} -\cos{(A+B)}]$
$10 \sin{5x} \sin{3x} = 5[\cos{2x} - \cos{8x}]$
Trigonometry 7th Edition
by McKeague, Charles P.; Turner, Mark D.
Published by
Cengage Learning
ISBN 10:
1111826854
ISBN 13:
978-1-11182-685-7
Chapter 5 - Section 5.5 - Additional Identities - 5.5 Problem Set - Page 311: 28
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