\[y = \sqrt{3x - x^{2}}\]
\[3x - x^{2} \geq 0\]
\[x^{2} - 3x \leq 0\]
\[x(x - 3) \leq 0\]
\[x = 0;\ \ x = 3.\]
\[Ответ:0 \leq x \leq 3.\ \]