6 The functions f and g are defined by
$$\begin{aligned}
& \mathrm { f } ( x ) = \frac { 2 } { x ^ { 2 } - 1 } \text { for } x < - 1
& \mathrm {~g} ( x ) = x ^ { 2 } + 1 \text { for } x > 0
\end{aligned}$$
- Find an expression for \(\mathrm { f } ^ { - 1 } ( x )\).
- Solve the equation \(\operatorname { gf } ( x ) = 5\).