1,ab(x^2+1)+x(a^2+b^2)=abx^2+x(a^2+b^2)+ab=(ax+b)(bx+a)2,4a^2-ab+b^2-c^2(题有误)3,9m^2-6m+2n-n^2=(3m-1)^2-(n-1)^2=(3m+n-2)(3m-n)4,（z^2-x^2-y^2）^2-4x^2y^2=(z^2-x^2-y^2+2xy)(z^2-x^2-y^2-2xy)=(z+x-y)(z...4a^2-4ab+b^2-c^2 我改过了4a^2-4ab+b^2-c^2 =(2a-b)^2-c^2=(2a-b+c)(2a-b-c)