Precalculus (10th Edition)

Published by Pearson
ISBN 10: 0-32197-907-9
ISBN 13: 978-0-32197-907-0

Chapter 7 - Analytic Trigonometry - 7.4 Trigonometric Identities - 7.4 Assess Your Understanding - Page 475: 5



Work Step by Step

We also know that $cos$, $sec$, are even functions, which means $f(-\theta)=f(\theta).$ Hence $cos(-\theta)=cos(\theta).$ Therefore $cos(-\theta)-cos(\theta)=0.$
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