(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)