\[f(x) = \frac{5}{3 - x}\]
\[3 - x \neq 0\]
\[x \neq 3.\]
\[f(x) = - 2,5:\]
\[- 2,5 = \frac{5}{3 - x}\]
\[- 2,5(3 - x) = 5\]
\[- 7,5 + 2,5x = 5\]
\[2,5x = 5 + 7,5\]
\[2,5x = 12,5\]
\[x = 12,\ 5\ :2,5 = 125\ :25\]
\[x = 5\ (существует).\]