5x^2-4xy+y^2-2x+1=0
(4x^2-4xy+y^2)+(x^2-2x+1)
=0
(2x-y)^2+(x-1)^2=0
2x-y=0,x-1=0
x=1,y=2.
(x-y)^2012=(1-2)^2012=1