1.-3ax^3+6ax^2y-3axy^2
=-3ax(x^2-2xy+y^2)
=-3ax(x-y)^2
2.4a^2-（a^2+1)^2
=(2a+a^2+1)(2a-a^2-1)
=-(a^2+2a+1)(a^2-2a+1)
=-(a+1)^2(a-1)^2