4x^2-64
=4(x^2-16)
=4(x+4)(x-4)
3x(a-b)-6y(b-a)
=3x(a-b)+6y(a-b)
=3(a-b)(x+2y)
9x^2-6x+1
=(3x-1)^2
4ab-4a^2b-b^2
=b(4a-4ab-b)