36. $y=\sqrt{2 x^{2}-6 x}$.
Solution. The domain of the function is found from the condition $2 x^{2}-6 x \geqslant 0$ or $2 x(x-3) \geqslant 0$. The solutions to this inequality are $x \leqslant 0, x \geqslant 3$. Therefore, the domain of the function consists of the half-intervals $(-\infty, 0]$ and $[3, \infty)$. This can be illustrated on a number line (Fig. 66).