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