Precalculus (10th Edition)

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

Chapter 6 - Trigonometric Functions - 6.3 Properties of the Trigonometric Functions - 6.3 Assess Your Understanding - Page 395: 90



Work Step by Step

We know that $\cos$ has a period of $2\pi$, hence $\cos(\theta)=\sin(\theta+2k\pi)$ where $k$ is an integer. Therefore, $\cos(\theta)+\cos(\theta+2\pi)+\cos(\theta+4\pi)\\ =\cos(\theta)+\cos(\theta)+\cos(\theta)\\ =0.2+0.2+0.2\\ =0.6$
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