\[y = \frac{7}{x - 5} - \frac{x}{x - 1};\]
\[x - 5 \neq 0\]
\[x \neq 5.\]
\[x - 1 \neq 0\]
\[x \neq 1.\]
\[D(y) = ( - \infty;1) \cup (1;5) \cup (5; + \infty).\]