x^2+y^2+z^2=xy+yz+xz 2(x^2+y^2+z^2)=2(xy+yz+xz) x^2+y^2-2xy+x^2+z^2-2xz+y^2+z^2-2yz=0 (x-y)^2+(y-z)^2+(x-z)^2=0 x-y=0 y-z=0 x-z=0 x=y=z
