\begin{frame}
  \frametitle{Computing Limits: Function Replacement}
  
  \begin{exampleblock}{}
    Find 
    \begin{talign}
      \lim_{h\to 0} \frac{(3+h)^2 - 9}{h}
    \end{talign}
    \pause
    We have:
    \begin{talign}
      \frac{(3+h)^2 - 9}{h} 
      \mpause[1]{ = \frac{9 + 6h + h^2 - 9}{h}}
      \mpause[2]{ = \frac{6h + h^2}{h}}
      \mpause[3]{ \stackrel{\text{\alert{for $h \ne 0$}}}{=} 6 + h } 
    \end{talign}
    \pause\pause\pause\pause
    As a consequence:
    \begin{talign}
      \lim_{h\to 0} \frac{(3+h)^2 - 9}{h}  = \lim_{h\to 0} (6+h) \mpause[1]{ = 6}
    \end{talign}
  \end{exampleblock}
\end{frame}