Answer
$\cos\theta\cos\phi +\sin\theta\sin\phi $
Work Step by Step
given that $\cos(\theta-\phi)$
we know that cosine of the difference $\cos(A-B)=\cos A \cos B+\sin A\sin B$
on comparing with the above formula
$\cos(\theta-\phi)$ =$\cos\theta\cos\phi +\sin\theta\sin\phi $
