x+y+3=0,x+y=-3
3分之2-2x-2y+（-x-y）的平方
=【2-2（x+y)+（x+y)^2】/3
=（2-6+9）/3
=5/3
（x+y）/xy=3,x+y=3xy
(2x-3xy+2y)/(-x+2xy-y)
=[2(x+y)-3xy]/[2xy-(x+y)]
=3xy/(-xy)
=-3