\[\boxed{\text{303\ (303).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[1)\ \sqrt{(a - b)^{2}};\ \ \ b \geq a\]
\[\sqrt{(a - b)^{2}} = |a - b| = b - a.\]
\[2)\ \sqrt{c^{2} + 6c + 9};\ \ c \geq - 3\]
\[\sqrt{c^{2} + 6c + 9} = \sqrt{(c + 3)^{2}} =\]
\[= |c + 3| = c + 3.\]
\[3)\ \frac{\sqrt{(m - 5)^{4}}}{m^{2} - 10m + 25} =\]
\[= \frac{(m - 5)^{2}}{(m - 5)^{2}} = 1.\]