Answer
The formula $\cos \alpha \sin \beta =\frac{1}{2}\left[ \sin \left( \alpha +\beta \right)-sin\left( \alpha -\beta \right) \right]$ can be used to change the product of a cosine and a sine into the difference of two sines expressions.
Work Step by Step
$\cos \alpha \sin \beta =\frac{1}{2}\left[ \sin \left( \alpha +\beta \right)-sin\left( \alpha -\beta \right) \right]$
Thus, the above identity or product sum formula reflects that the product of a cosine and sines is equal to the half of the difference of the two sines expression.
