sin10°^2+cos40°^2+sin10°sin40°
=1/2(1-cos20)+1/2(1+cos80)+1/2(cos20-cos60)
=3/4+1/2*cos80
题目估计抄错了
估计是这样：
sin10°^2+cos40°^2+sin10°cos40°
=1/2(1-cos20)+1/2(1+cos80)+1/2(sin50-sin30)
=3/4-1/2(cos20-cos80)+1/2sin50
=3/4-sin30*sin50+1/2sin50
=3/4