25x y^2 z^2 (x+y-z)-30xyz(z-x-y)^2+5x y z^3 (z-x-y)
=25x y^2 z^2 (x+y-z)+30xyz(x+y-z)^2-5x y z^3 (x+y-z)
=5xyz(x+y-z)[5yz+6(x+y-z)-z^2]