P
pe_chau_hocgioi


(x + a)(x + 2a)(x + 3a)(x + 4a) + a^4
(x^2 + y^2 + z^2)(x + y + z)^2 + (xy + yz + zx)^2
2(x^4 + y^4 + z^4) - (x^2 + y^2 + z^2)^2 - 2(x^2 + y^2 + z^2)(x + y + z)^2 + (x + y + z)^4
(x^2 + y^2 + z^2)(x + y + z)^2 + (xy + yz + zx)^2
2(x^4 + y^4 + z^4) - (x^2 + y^2 + z^2)^2 - 2(x^2 + y^2 + z^2)(x + y + z)^2 + (x + y + z)^4