\[\boxed{\mathbf{830}\mathbf{.}}\]
\[f(x) = \sqrt{x^{2} - 5x + 6}\]
\[u = x^{2} - 5x + 6\ f(u) = \sqrt{u}:\]
\[f^{'}(x) = \left( x^{2} - 5x + 6 \right)^{'} \bullet \left( \sqrt{u} \right)^{'} =\]
\[= (2x - 5) \bullet \frac{1}{2\sqrt{u}} =\]
\[= \frac{2x - 5}{2\sqrt{x^{2} - 5x + 6}}.\]
\[x^{2} - 5x + 6 > 0\]
\[D = 25 - 24 = 1\]
\[x_{1} = \frac{5 - 1}{2} = 2\]
\[x_{2} = \frac{5 + 1}{2} = 3\]
\[(x - 2)(x - 3) > 0\]
\[x < 2\ или\ x > 3.\]
\[Ответ:\ \ \frac{2x - 5}{2\sqrt{(x - 2)(x - 3)}}.\]