cos^2 80°+sin^2 50°-sin190°cos320°
问题描述：
cos^2 80°+sin^2 50°-sin190°cos320°
答
cos^2 80°+sin^2 50°-sin190°cos320
=sin10^2+sin50^2-sin(180+10)cos(360-40)
=sin10^2+cos40^2+sin10cos40
设sin10=x,cos40=y
=x^2+y^2+xy
=(x+y)^2-xy