-x^2-2y^2-2x+8y-5
=-(x^2+2x+1-1)-2(y^2-4y+4-4)-5
=-(x+1)^2+1-2(y-2)^2+8-5
= -(x+1)^2-2(y-2)^2+4
最大值为4,x=-1 y=2