 matrix are the <em>partial derivatives</em> of $V$.</p>
        
        </li>
      <li>
          If we know that $r=3$ and $h=4$, and we know that
        $r$ increases by about $.1$ and $h$ increases by about
        $.2$, then approximate how much $V$ will increase. Use your
        formula for $dV$ to approximate this.
      </li>
    </ol>
  </div>

  <div class="problem">
    The volume of a box is $V(x,y,z)=xyz$. Imagine that each
    variable depends on $t$.

    <ol>
      <li>If both $y$ and $z