 were standing at $\vec r(3,\pi)$ and someone told
      you, &ldquo;Hey you, hold $t$ constant and increase
      $a$,&rdquo; then in which direction would you move? What
      if someone told you, &ldquo;Hey you, hold $a$ constant and
      increase $t$&rdquo;?</li>

      <li>Give vector equations for two tangent lines to the
      surface at $\vec r(3,\pi)$. [Hint: You've got the point by
      plugging $(3,\pi)$ into $\vec r$, and you've got two
      different direction vectors from $D\vec r$. Once yo