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\begin{frame}
  \frametitle{Derivatives and the Shape of a Graph}

  Recall Fermat's Theorem
  \begin{block}{}
    If $f$ has a local extremum at $c$, then $c$ is a critical number.
  \end{block}
  \pause\bigskip
  
  But not ever critical number is an extremum. \pause We need a test!
\end{frame}