x²y+y²z+z²x-x²z-y²x-z²y=(x²y-x²z)+(y²z-z²y)+(z²x-y²x)=x²(y-z)+yz(y-z)+x(z-y)(z+y)=(y-z)(x²+yz-xz-xy)=(y-z)[x(x-z)+y(z-x)]=(y-z)(x-...