第一个-a^b^2+2a^2b^2-a^2
=a^2b^2-a^2
=a^2(b^2-1)
=a^2(b+1)(b-1)
第二个4ax^2-16ay^2
=4a(x^2-4y^2)
=4a(x+2y)(x-2y)