Maybe use some triple angle formula? Look here.
Double & Triple Angle formulas
Maybe use some triple angle formula? Look here.
Double & Triple Angle formulas
I've tried using the Product-to-sum formula, but it only makes things more confusing (to me). My teacher said that we should be able to solve this only using the addition/subtraction formulas.
and this is what I have gotten so far
[Cosx (cos^2x - sin^2x) cosx - (2sinxcosx) sinx] - [sinx (2sinxcosx) cosx + (cos^2x - sin^2x) sinx]
I don't know if that is right, I'm still playing around with what what I have.