ction $f(x,y)=y-x^2$.

    <ol>
      <li>In the $xy$ plane, please draw several level curves of
      $f$ (maybe $z=0$, $z=2$, $z=-4$, etc.) Write the height on
      each curve (so you're making a contour plot).</li>

      <li>Compute the derivative $Df$ (which we'll think of as a
      vector field).</li>

      <li>
        <div class="marginpar">
          We'll examine the connection between the derivative and
          level curves much more when we study optimization later.
        </div>Pick 8 poi