\[\boxed{\mathbf{24}\mathbf{.}}\]
\[\textbf{а)}\ y = \sqrt{x^{2} + 6x + 9} =\]
\[= \sqrt{(x + 3)^{2}} = |x + 3|\]
\[\textbf{б)}\ y = \sqrt{4x^{2} - 4x + 1} =\]
\[= \sqrt{(2x - 1)^{2}} = |2x - 1|\]
\[\textbf{в)}\ y = \sqrt{- x^{2} + x + 6}\]
\[y^{2} = - x^{2} + x + 6\]
\[y^{2} + x^{2} - x = 6\]
\[y^{2} + x^{2} - x + \frac{1}{4} - \frac{1}{4} = 6\]
\[y^{2} + \left( x - \frac{1}{2} \right)^{2} = 6 + \frac{1}{4}\]
\[\left( x - \frac{1}{2} \right)^{2} + y^{2} = \frac{25}{4}\]
\[окружность\ O\left( \frac{1}{2};0 \right);\ \ R = \frac{5}{2}.\]
\[\textbf{г)}\ y = \sqrt{- x^{2} + 2x + 8}\]
\[y^{2} = - x^{2} + 2x + 8\]
\[y^{2} + x^{2} - 2x = 8\]
\[y^{2} + x^{2} - 2x + 1 - 1 = 8\]
\[y^{2} + (x - 1)^{2} = 8 + 1\]
\[(x - 1)^{2} + y^{2} = 9\]
\[окружность\ O(1;0);\ \ R = 3.\]