原式
=[(x^2-2xz+z^2)-y^2][(x^2+2xz+y^2)-y^2]
=[(x-z)^2-y^2][(x+z)^2-y^2]
=(x-z+y)(x-z-y)(x+y+z)(x-y+z)
狂用平方差公式