so $u=2$ and $v=\pi/2$).</li>

      <li>Give a normal vector to the surface at $\vec
      r(2,\pi/2)$.</li>

      <li>Give an equation of the tangent plane at $\vec
      r(2,\pi/2)$.</li>
    </ol>
  </div>
    <p>We now have two different ways to compute tangent planes.
  One way generalizes differential notation $dy=f'dx$ to $dz = Df
  \begin{bmatrix}dx\\dy\end{bmatrix}$ and then uses matrix
  multiplication. This way will extend to tangent objects in EVERY
  dimension. It's the key idea needed to wor