#### Answer

$-\cos\theta$

#### Work Step by Step

Use the subtraction formula for cosine, $\cos (A-B)=\cos A\cos B+\sin A\sin B$:
$\cos(\theta-180^\circ)$
$=\cos\theta\cos 180^\circ+\sin\theta\sin 180^\circ$
$=\cos\theta*(-1)+\sin\theta*0$
$=-\cos\theta$

Published by
Pearson

ISBN 10:
013421742X

ISBN 13:
978-0-13421-742-0

$-\cos\theta$

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