Answer
See below.
Work Step by Step
$LHS=cos(\theta+k\pi)=cos\theta cos(k\pi)-sin\theta sin(k\pi)=cos\theta cos(k\pi)=(-1)^k cos\theta =RHS$
Precalculus (10th Edition)
by Sullivan, Michael
Published by
Pearson
ISBN 10:
0-32197-907-9
ISBN 13:
978-0-32197-907-0
Chapter 7 - Analytic Trigonometry - 7.5 Sum and Difference Formulas - 7.5 Assess Your Understanding - Page 488: 74
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