First off I know how to do things such as,
cosx x cos 4x = (1/2) x (cos(x+4x) + cos(x-4x))
= (1/2) x (cos 5x) x (cos(-3x))
However i'm getting very confused over one simple difference which is,
2 sin5x . sin2x, as in what do I with the 2 out the front of this equation?
This is what I tried (I have no idea though if its right or wrong)
(2 sin5x . sin2x) = (1/2)x(2) x (sin(5x+2x) + (cos5x-2x))
= (sin 7x) + (cos3x)
Any help would be great.