三角函数之求值问题sin²20°+cos²50°+sin20°cos50°=sin20°cos50 应该变为-sin30°+sin70 -3/4
网友回答
sin²20°+cos²50°+sin20°cos50°
=(1-cos40°)/2+(1+cos100°)/2+（-sin30°+sin70°）/2
=1+1/2(cos100°-cos40°）+（-sin30°+sin70°）/2
=1-sin70°*sin30°+（-sin30°+sin70°）/2
=1-(1/2)sin70°-1/4+(1/2)sin70°
=3/4此题主要时积化和差,和差积化的转换运用!