Answer
See the steps.
Work Step by Step
$\cos{(180-\theta)} = \cos{180} \cos{\theta} + \sin{180} \sin{\theta}$
$\cos{(180-\theta)} = -1 \times \cos{\theta} + 0 \times \sin{\theta} = - \cos{\theta}$
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 288: 21
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