（cosθ）^2-（cosθ）^4 = 1-(sinθ)^2-{1-(sinθ)^2}^2=1-(sinθ)^2-{1-(sinθ)^2}^2=
1-(sinθ)^2-1+2(sinθ)^2-(sinθ)^4=(sinθ)^2-(sinθ)^4