\(\left(x-y\right)^3+\left(y-z\right)^3+\left(z-x\right)^3\)
\(=\left(x-y+y-z\right)^3-3\left(x-y\right)\left(y-z\right)\left(x-y+y-z\right)-\left(x-z\right)^3\)
\(=\left(x-z\right)^3-3\left(x-y\right)\left(y-z\right)\left(x-z\right)-\left(x-z\right)^3\)
=-3(x-y)(y-z)(x-z)