cos74°sin14°-sin74°cos14°=?sin20°cos110°+cos160°sin70°=?要详解

cos74°sin14°-sin74°cos14°= - (sin74°cos14°-cos74°sin14°)=-sin(74°-14°)=-sin60°sin20°cos110°+cos160°sin70°=sin20°cos(90°+20°）+cos(90°+70°)sin70°=sin20°(cos90°cos20°-sin90°sin2...