vatives vectors). Explain.</li>
    </ol>
  </div><p>If your answers to the 2nd and 3rd part above were the
  same, then you're doing this correctly. The partial derivatives
  of parametric functions tell us about motion and tangents. The
  next problem reinforces this concept. But first, a short review
  about equations of lines.</p>

  <div class="review">
    If you know that a line passes through the point $(1,2,3)$ and
    is parallel to the vector $(4,5,6)$, give a vector equation,
    and parametric 