化简有sinθ=cos^2θ
同时乘以sinθ
sin^2θ+sin^3θ=sinθ
∴sin^3θ=sinθ-sin^2θ=cos^2θ-sin^2θ=cos2θ
∴=sinθ+sin^2θ+sin^3θ
=1+sin^3θ
=1+cos2θ
=2cos^2θ
=2sinθ
又sin²θ+sinθ-1=0 解出