(x^2+y^2-z^2)^2-4x^2y^2
利用平方差公式
(x^2+y^2-z^2)^2-4x^2y^2
=[(x^2+y^2-z^2)+2xy][(x^2+y^2-z^2)-2xy]
=[x^2+y^2+2xy-z^2][x^2-2xy+y^2-z^2]
=[(x+y)^2-z^2][(x-y)^2-z^2]
=(x+y+z)(x+y-z)(x-y+z)(x-y-z)
(x^2+y^2-z^2)^2-4x^2y^2
利用平方差公式
(x^2+y^2-z^2)^2-4x^2y^2
=[(x^2+y^2-z^2)+2xy][(x^2+y^2-z^2)-2xy]
=[x^2+y^2+2xy-z^2][x^2-2xy+y^2-z^2]
=[(x+y)^2-z^2][(x-y)^2-z^2]
=(x+y+z)(x+y-z)(x-y+z)(x-y-z)