1-sin^6θ-cos^6θ
= sin^2θ(1-sin^4θ) + cos^2θ(1-cos^4θ)
= sin^2θ[sin^2θ(1-sin^2θ) + cos^2θ] + cos^2θ[cos^2θ(1-cos^2θ)+sin^2θ]
=sin^2θ*cos^2θ*(1+sin^2θ) + sin^2θ*cos^2θ*(1+cos^2θ)
=sin^2θ*cos^2θ*(1+1+sin^2θ+cos^2θ)
=3sin^2θ*cos^2θ
sin^2θ-sin^4θ
=sin^2θ*(1-sin^2θ)
=sin^2θ*cos^2θ
分子/分母 = 3