\[1)\ f(x) = \frac{1}{x^{2} - 9}\]
\[x^{2} - 9 = 0\]
\[x^{2} = 9\]
\[x = \pm 3.\]
\[Ответ:\ - 3;\ 3.\]
\[2)\ f(x) = \frac{x + 2}{3x + 1}\]
\[3x + 1 = 0\]
\[3x = - 1\]
\[x = - \frac{1}{3}.\]
\[Ответ:\ - \frac{1}{3}.\]