(square of a-2a) (square of a-2a-6) + 9

(square of a-2a) (square of a-2a-6) + 9

Original formula = (a ^ 2-2a) ^ 2-6 (a ^ 2-2a) + 9
=(a^2-2a-3)^2
=[(a-3)(a+1)]^2
=(a-3)^2(a+1)^2