(cos x)^4-(sin x)^4-2(sin x)(cos x)=[(cos x)^2+(sin x)^2]*[(cos x)^2-(sin x)^2]-sin 2x=1*cos 2x-sin 2x=√2((√2/2)cos 2x-(√2/2)sin 2x)=√2sin (2x-45°)