x^2+1／2y⒉+4≤xy+2y
x^2+1／2y^2+4-xy-2y<=0
(x-y/2)^2+y^2/4-2y+4<=0
(x-y/2)^2+(y/2-2)^2<=0
x-y/2=0, y/2-2=0
y=4, x=2.