Question

sin的平方20度+cos的平方50度+sin20度*cos50度=

Answer 1

用倍差及积化和差,得0.5*（1-cos40）+0.5*(1+cos100)+0.5*(sin70-sin30)=1-0.5*cos(70-30)+0.5*cos(70+30)+0.5*(sin70-0.5)=0.75