m/input/?i=parametric+plot+3D++/%28a+cos+t/%2C+a+sin+t/%2C+t/%29+for+t+from+0+to+4+pi+and+a+from+2+to+4">
          Wolfram Alpha</a> for a plot of the surface. Click on
          either link.
        </div>Look at a plot of the surface (use one of the links
        to the right). Now, suppose an object is on this surface at
        the point $\vec r(3,\pi) = (-3,0,\pi)$. At that point,
        please draw the partial derivatives $\vec r_a(3,\pi)$ and
        $\vec r_t(3,\pi)$.
      </li>

      <li>If you