\begin{frame}
  \frametitle{Infinite Limits at Infinity}

  \begin{exampleblock}{}
    Evaluate
    \begin{talign}
      \lim_{x\to\infty} (x^2 - x)
    \end{talign}
    \pause
    The limit laws do not help since:
    \begin{talign}
      \lim_{x\to\infty} (x^2 - x) 
      \mpause[1]{= \lim_{x\to\infty} x^2 - \lim_{x\to\infty} x}
      \mpause[2]{= \infty - \infty}
      \mpause[3]{= \alert{\text{invalid expression}}}
    \end{talign}
    \pause\pause\pause\pause
    However, we can write
    \begin{talign}
      \lim_{x\to\infty} (x^2 - x) 
      \mpause[1]{= \lim_{x\to\infty} x(x - 1) }
      \mpause[2]{= \infty}
    \end{talign}
    \pause\pause\pause
    because both $x$ and $x-1$ become arbitrarily large.  
  \end{exampleblock}
\end{frame}