因式分 （1） （z²-x²-y²）²-4x²y² =(z^2-x^2-y^2-2xy)(z^2-x^2-y^2+2xy) =[z^2-(x+y)^2][z^2-(x-y)^2] =(z-x-y)(z+x+y)(z-x+y)(z+x-y) .