解1：cos80°sin70°+sin80°sin20°=cos80°sin(90°-20°)+sin80°sin20=cos80°cos20°+sin80°sin20°=cos(80°-20°)=cos60°=1/2解2：cos80°sin70°+sin80°sin20°=cos80°sin70°+sin80°sin(90°-70°)=co...