Answer
$-\cos\theta$
Work Step by Step
Use the subtraction formula for cosine, $\cos (A+B)=\cos A\cos B-\sin A\sin B$:
$\cos(180^\circ+\theta)$
$=\cos 180^\circ\cos \theta-\sin 180^\circ\sin \theta$
$=-1*\cos\theta-0*\sin\theta$
$=-\cos\theta$
Precalculus (6th Edition)
by Lial, Margaret L.; Hornsby, John; Schneider, David I.; Daniels, Callie
Published by
Pearson
ISBN 10:
013421742X
ISBN 13:
978-0-13421-742-0
Chapter 7 - Trigonometric Identities and Equations - 7.3 Sum and Difference Identities - 7.3 Exercises - Page 680: 65
Update this answer!
You can help us out by revising, improving and updating this answer.
Update this answerAfter 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.
