$$\frac { d } { d x } ( f ^ { - 1 } ( x ) ) f ( x ) = x ^ { 2 }$$
$f\neq 0$
$\left(x=2\text{ or }x=0\right)\text{ and }f\neq 0$
$x=2$
$x=0\text{, }f\neq 0$
