tial derivatives of parametric functions</h1>
                <p>Now let's
  examine computations similar to those in <a href=
  "#cake-introduction">this problem</a> in the light of parametric
  surfaces. With parametric functions, partial derivatives are
  vectors instead of just numbers. But they still represent how the
  outputs change relative to changes in the inputs.</p>

  <div class="problem">
    <div class="marginpar">
      See <a href=
      "https://sagecell.sagemath.org/?z=eJx9kUtvAiEYRff8CqI