cos²（50°+α）+cos²（40°-α）-tan(30°-α)tan(60°+α)=?
问题描述：
cos²（50°+α）+cos²（40°-α）-tan(30°-α)tan(60°+α)=?
答
tan(30°-α)=cot[90°-(30°-α)]=cot(60°+α)tan(30°-α)tan(60°+α)=cot(60°+α)tan(60°+α)=1同理：cos2（40°-α）=sin2[90°-（40°-α）]=sin2（50°+α）cos2（50°+α）+cos2（40°-α）=cos2（50°+...