Question

Write these products as sums:

cos(2x)sin(5x)

Answer 1

@AravindG
@Mertsj
@amistre64

Answer 2

\[\cos A\sin B=\frac{1}{2}(\sin(A+B)-\sin(A-B))\Rightarrow\\
\Rightarrow \cos 2x\sin 5x=\frac{1}{2}(\sin(7x)-\sin(-3x))=\\
=\frac{1}{2}(\sin(7x)+\sin(3x))\]