Answer
See the steps.
Work Step by Step
$\cos{(A+B)} + \cos({A-B}) =$
$$\cos{A} \cos{B} - \sin{A} \sin{B} + \cos{A} \cos{B} + \sin{A} \sin{B} $$
$LHS = 2 \cos{A} \cos{B} = RHS$
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 5.2 - Sum and Difference Formulas - 5.2 Problem Set - Page 290: 62
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