(tan5°-cos5°/sin5°)*(cos20°-1)/cos°70
问题描述：
(tan5°-cos5°/sin5°)*(cos20°-1)/cos°70
答
cos20=sin70 原式=(sin5/cos5-cos5/sin5)cos70/(1+sin70) =[(sin5)^2-(cos5)^2]/sin5/cos5*cos70/(1+sin70) =-2cos10/sin10*sin20