Answer
$(x+4)(x-4)(a-2)$
Work Step by Step
The product of a binomial sum and a binomial difference is: $(A+B)(A-B)=A^2-B^2$.
The square of a binomial sum is: $(A+B)^2=A^2+2AB+B^2$.
The square of a binomial difference is: $(A-B)^2=A^2-2AB+B^2$.
Hence here: $ax^2-16a-2x^2+32=\\=a(x^2-16)-2(x^2-16)\\=(x^2-16)(a-2)\\=(x^2-4^2)(a-2)\\=(x+4)(x-4)(a-2)$