

    <ol>
      <li>Compute the partial derivatives $\vec r_a$ and $\vec r_t$
      (they are vectors), and state the total derivative. (How big
      is the matrix? What is the domain and range of $\vec
      r$?)</li>

      <li>  
        <div class="marginpar">
          Please see <a href=
          "https://sagecell.sagemath.org/?z=eJxL0yjRUUjUtNVI1ErOL9Yo0QTytIoz88CsEk2ugsSixNzUkqLM5PiCnPwSjTQdBaAOAx0FE62CTKASjUQdBSMgT1OTCwBCiRSf">
          Sage</a> or <a href=
          "http://www.wolframalpha.co