$\begin{array}{l} a)a - 16\left( {BS:a > 0} \right)\\ = \left( {\sqrt a - 4} \right)\left( {\sqrt a + 4} \right)\\ b)25{a^2} - 11 = \left( {5a - \sqrt {11} } \right)\left( {5a + \sqrt {11} } \right)\\ c)4 + 3a\left( {a < 0} \right) = 4 - \left( { - 3a} \right) = \left( {2 - \sqrt { - 3a} } \right)\left( {\sqrt 2 + \sqrt { - 3a} } \right)\\ d)m - 2\sqrt m + 1 - {n^2}\\ = \left( {m - 2\sqrt m + 1} \right) - {n^2}\\ = {\left( {\sqrt m - 1} \right)^2} - {n^2} = \left( {\sqrt m - n - 1} \right)\left( {\sqrt m - 1 + n} \right)\\ e)4a - 4\sqrt a + 1 - {a^2}\\ = {\left( {2\sqrt a - 1} \right)^2} - {a^2} = \left( {2\sqrt a - 1 - a} \right)\left( {2\sqrt a - 1 + a} \right)\\ f)x - 3\sqrt x + 2 = x - \sqrt x - 2\sqrt x + 2\\ = \sqrt x \left( {\sqrt x - 1} \right) - 2\left( {\sqrt x - 1} \right)\\ = \left( {\sqrt x - 1} \right)\left( {\sqrt x - 2} \right) \end{array}$
