13x^2—6xy+y^2—4x+1=0
(3x-y)^2+(2x-1)^2=0
2x-1=0,x=1/2
3x-y=0,y=3x=3*1/2=3/2
y-x=3/2-1/2=1
x*(y-x)=1/2*1=1/2
(1/2)^3=1/8
(xy-x^2）^3=[x*(y-x）]^3=(1/2)^3=1/8