9 The function \(\mathrm { f } ( x ) = \frac { \mathrm { e } ^ { x } } { 1 - \mathrm { e } ^ { x } }\) is defined on the domain \(x \in \mathbb { R } , x \neq 0\).
- Find \(\mathrm { f } ^ { - 1 } ( x )\).
- Write down the range of \(\mathrm { f } ^ { - 1 } ( x )\).