Find a formula for $f^{-1}(x)$ if $\displaystyle f(x) = \left( {\frac{x - 1}{x + 1}} \right)^3$

$f^{-1}(x)$ = .

$\left(f^{-1}\right)'(x) =$ .

Hint: Undo the operations of $f(x)$ from the outside in. Undo the cubed operation first.