x^2+y^2-2x+6y+10
=(x-1)^2+(y+3)^2=0
x=1,y=-3
(x-y)^2-(x^2-y^2)
=(x-y)^2-(x+y)(x-y)
=(x-y)(x-y-x-y)
=(x-y)*(-2y)
=(1-(-3))*(-2*(-3))
=4*6
=24