Question

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

Answer 1

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°sin20°）+(cos90°cos70°-sin90°sin70°)sin70°
=-sin20°sin20°-sin70°sin70°=-sin220°-sin270°=-sin220°-sin2(90-20)°=-1

Answer 2

楼上的是错的
cos74sin14-sin74cos14
=sin14cos74-cos14sin74
=sin(14-74)
=sin(-60)
=-sin60
=-√3/2