1-cos ^2x=sin^2x 方程两边同时乘以sinx^2/cosx^2 sin^2x/cos^2x - sin^2x =sin^2x sin^2x/cos^2x tan^2x -sin^2x =sin^2 x tan^2 x (tanx-sinx)(tanx+sinx)=(sinx tanx) (sinx tanx) 两边分别除以sinxtanx/(tanx+si...