\[f(x) = \frac{x - 4}{x^{2} - x - 6}\]
\[x^{2} - x - 6 \neq 0\]
\[D = 1 + 24 = 25\]
\[x_{1} = \frac{1 + 5}{2} = 3;x_{2} = \frac{1 - 5}{2} = - 2.\]
\[D(y) = ( - \infty; - 2) \cup ( - 2;3) \cup (3; + \infty).\]