Here's the question you clicked on:
marasofia1616
Verify the identity. sin (x + y) - sin (x - y) = 2 cos x sin y
do you know the formula for sin(A+B) =... ?
Sin(a+b) = sin a . cos b + Cos a. Sin b sin (a-b) = sin a . cos b - Cos a. Sin b
Yeah, that's pretty much it ^