Su1RF1Trzgjv1wDaARIq3EKNs2aALkvIzE=">
      Sage</a> or <a href="http://www.wolframalpha.com/input/?i=plot+%28x%5E2-y%5E2%29%2F%28x%5E2%2By%5E2%29">Wolfram
      Alpha</a> (try using the &ldquo;contour lines&rdquo;
      option).
      As you compute each limit, make sure you understand what that
      limit means in the graph.
    </div>
      Our goal is to determine if the function has a limit at
    the origin $(0,0)$.

    <ol>
      <li>In the $xy$-plane, how many lines pass through the origin
      $