(sina+cosa-1)(sina-cosa+1)/sin2a = tana/2 证明
问题描述：
(sina+cosa-1)(sina-cosa+1)/sin2a = tana/2 证明
答
(sina+cosa-1)(sina-cosa+1)/sin2a=[sina^2-(cosa-1)^2]/sin2a=[sina^2-cosa^2+2cosa-1]/sin2a=[-2cosa^2+2cosa]/sin2a=[-2cosa^2+2cosa]/(2sina*cosa)=[-cosa+1]/sina=tan(a/2)