y,z)=w$</li>

      <li>$\vec r(t)=(x,y,z)$</li>

      <li>$\vec r(u,v)=(x,y,z)$</li>

      <li>$\vec F(x,y)=(M,N)$</li>

      <li>$\vec F(\rho,\phi,\theta)=(x,y,z)$</li>
    </ol>
  </div>
                <p>You learned to work with limits in first-semester calculus
  without needing the formal definitions above. Many of those
  techniques apply in higher dimensions. The following problem has
  you review some of these technique, and apply them in higher
  dimensions.</p>

  <div class="problem">
    <d