1. a^2 + 8ab + 16b^2 - 1 =
(а + 4b)^2 - 1 =
(а + 4b - 1) * (а + 4b+1)
2. ax^6 - 3x^6 - ax^3 + 3x^3 =
x^3 * (ax^3 - 3x^3 - a + 3) =
x^3 * (x^3 * (a - 3) - (a - 3)) =
x^3 * (x^3 - 1) * (a - 3)
3. 25 -m^2 - 12mn - 36n^2 =
25 - (36n^2 + 12mn + m^2) =
5^2 - (6n + m)^2 =
(5 - 6n - m) * (5 + 6n +m)