sin²20°＋cos²50°＋sin20°cos50°＝＿＿? 能告诉我过程吗?
问题描述：
sin²20°＋cos²50°＋sin20°cos50°＝＿＿? 能告诉我过程吗?
答
sin²20°+cos²50°+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-(cos6...