求值（tan5°-cos5°）sin20°/1+cos20°
问题描述：
求值（tan5°-cos5°）sin20°/1+cos20°
答
（tan5°-cot5°）sin20°/(1+cos20°)=(sin5º/cos5º-cos5º/sin5º)/(2cos²10º)=[(sin²5º-cos²5º)/(sin5ºcos5º)]/(2cos²10º)=-2[(cos10º...