9 A function f is defined by \(\mathrm { f } ( x ) = \frac { 5 } { 1 - 3 x }\), for \(x \geqslant 1\).
- Find an expression for \(\mathrm { f } ^ { \prime } ( x )\).
- Determine, with a reason, whether \(f\) is an increasing function, a decreasing function or neither.
- Find an expression for \(\mathrm { f } ^ { - 1 } ( x )\), and state the domain and range of \(\mathrm { f } ^ { - 1 }\).