>>582
(x^2y^2)+(x^2z^2)+(-y^2z^2)+(2x^2yz)
= (xy)^2+(xz)^2+2(xy)(xz) - (yz)^2
= (xy +xz)^2 -(yz)^2
= (xy +xz +yz)(xy+xz-yz)

普通に和と差の積（´・ω・｀）