Maybe use some triple angle formula? Look here.
Double & Triple Angle 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.