(x-y)^3+(y-z)^3+(z-x)^3
=[(x-y)^3+(y-z)^3]+(z-x)^3
=(x-y+y-z)[(x-y)^2-(x-y)(y-z)+(y-z)^2]+(z-x)^3
=(x-z)(3y^2-3xy+3xz-3yz)
=3(x-z)(x-y)(z-y)