Trigonometry (10th Edition)

Published by Pearson
ISBN 10: 0321671775
ISBN 13: 978-0-32167-177-6

Chapter 5 - Trigonometric Identities - Section 5.1 Fundamental Identities - 5.1 Exercises - Page 196: 89

Answer

$$y=\cos(-4x)=\cos 4x$$

Work Step by Step

$$y=\cos(-4x)$$ - According to Negative-Angle Identity: $$\cos(-x)=\cos x$$ Therefore, applying to the function here, we have $$y=\cos(-4x)=\cos 4x$$
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