## Precalculus (6th Edition)

$\frac{\cos\theta-\sqrt{3}\sin\theta}{2}$
Use the addition formula for cosine, $\cos (A+B)=\cos A\cos B-\sin A\sin B$: $\cos(60^\circ+\theta)$ $=\cos 60^\circ\cos \theta-\sin 60^\circ\sin \theta$ $=\frac{1}{2}*\cos\theta-\frac{\sqrt{3}}{2}*\sin\theta$ $=\frac{\cos\theta}{2}-\frac{\sqrt{3}\sin\theta}{2}$ $=\frac{\cos\theta-\sqrt{3}\sin\theta}{2}$