\[y = \sqrt{18x^{2} - 3x}\]
\[18x^{2} - 3x \geq 0\]
\[18x\left( x - \frac{1}{6} \right) \geq 0\]
\[x = 0;\ \ x = \frac{1}{6}\]
\[Ответ:x \leq 0;\ \ x \geq \frac{1}{6}\text{.\ }\]