Answer
See the steps.
Work Step by Step
$LHS = \cos^4{x}-\sin^4{x} = (\cos^2{x}+\sin^2{x})(\cos^2{x}-\sin^2{x})$
$LHS= (1) (\cos{2x}) = \cos{2x} = RHS$
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 5.3 - Double-Angle Formulas - 5.3 Problem Set - Page 297: 53
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