Question 707942
9b^2 - 24b + 16 - a^2


(9b^2 - 24b + 16) - a^2


(9b^2 - 12b - 12b + 16) - a^2


((9b^2 - 12b) + (-12b + 16)) - a^2


(3b(3b - 4) - 4(3b - 4)) - a^2


(3b - 4)(3b - 4) - a^2


(3b - 4)^2 - a^2


(3b - 4 - a)(3b - 4 + a)


So 9b^2 - 24b + 16 - a^2 completely factors to <font color="red">(3b - 4 - a)(3b - 4 + a)</font>