d,ta có
:z-x=(z-y)+(y-x).nên:
x^2y^2(y-x)+y^2z^2(z-y)-z^2x^2[(z-y)+(y-x)]
=x^2y^2(y-x)+y^2z^2(z-y)-z^2x^2(z-y)-z^2x^2(y-x)
=(y-x)(x^2y^2-z^2x^2)-(y-z)(y^2z^2-z^2x^2)
=(y-x)(x^2(y-z)(y+z)-(y-z)z^2(y-x)(y+x)
=(y-x)(y-z)(x^2y+x^2z-yz^2-x^2z)
=(y-x)(y-z)[xz(x-z)+y(x-z)(x+z)]
=(y-x)(y-z)(x-z)(xy+yz+xz)