\begin{deloppgaver}
  \delo
    \[f'(x) = 3\]

  \delo
    \[f^{-1}(x) = \frac{x}{3} - 1\]
  
  \delo
    \[\frac{d}{dx} f^{-1}(x) = \frac{1}{3} \]
  
\end{deloppgaver}