\[y = \sqrt{6x - 3x^{2}}\]
\[6x - 3x^{2} \geq 0\]
\[- 3x(x - 2) \geq 0\]
\[x = 0;\ \ x = 2\]
\[D(y) = x \in \lbrack 0;2\rbrack.\]