x^2+2xy+y^2=25 ===> (x+y)^2=5^2 ===> x+y=±5
(x-y)^2-3x+3y+2=0
===> (x-y)^2-3(x-y)+2=0
===> [(x-y)-1]*[(x-y)-2]=0
===> x-y=1,或者x-y=2
又,x+y=5,或者x+y=-5
联立解得：
x=3,y=2；
x=-2,y=-3；
x=7/2,y=3/2；
x=-3/2,y=-7/2.