sin20度平方+cos50度平方+sin20度cos50度=?

题目

sin20度平方+cos50度平方+sin20度cos50度=?

答案

0.75 追问：算法 回答：sin20°+cos50°+sin20°cos50° =(1-cos40°)/2+(1+cos100°)/2+(1/2)*(sin70°-sin30°) =(1-cos40°)/2+(1-cos80°)/2+(1/2)*(cos20°-1/2) =1-(1/2)*(cos40°+cos80°)+(1/2)*(cos20°-1/2) =1-(cos60°cos20°)+(1/2)cos20°-1/4 =1-(1/2)cos20°+(1/2)cos20°-1/4 =3/4 还一种方法：sin20°+cos50°+sin20°cos50° =sin20°+cos(20°+30°)+sin20°cos(20°+30°) 自己算一下吧