sinθ+sin^2θ=1,sin^2θ+cos^2θ=1∴sinθ=cos^2θ等式两边同时乘以sinθ有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根...