Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 7 - Section 7.5 - More Trigonometric Equations - 7.5 Exercises - Page 575: 40


$\frac{\pi}{3}$, $\frac{5\pi}{3}$

Work Step by Step

$\cos \theta\cos 2\theta+\sin \theta\sin 2\theta=\frac{1}{2}$ $\cos (\theta-2\theta)=\frac{1}{2}$ $\cos (-\theta)=\frac{1}{2}$ Since cosine is an even function, $\cos \theta=\frac{1}{2}$. The only solutions in $[0, 2\pi)$ are $\frac{\pi}{3}$ and $\frac{5\pi}{3}$.
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.