sin^2 10°+ sin^2 50°+ sin10°sin50°
问题描述：
sin^2 10°+ sin^2 50°+ sin10°sin50°
计算 ,
答
3/4.sin^2 10°+ sin^2 50°+ sin10°sin50°=（1-cos20）/2+（1-cos100)/2+(cos40-cos60)/2=(2-cos20-cos60+cos100+cos40)/2=(2-cos20-cos60+2cos60cos20)/2=(2-cos20-cos60+cos20)/2=(2-1/2)/2=3/4