mp;?\end{bmatrix}$. At the point
      $(x,y)=(2,1)$, the derivative is $Df(2,1) =
      \begin{bmatrix}-4&amp;?\end{bmatrix}$ and the output $z$ is
      $z=f(2,1)=?$.</li>

      <li>If we move from the point $(2,1,f(2,1))$ to the point
      $(x,y,z)$ along the tangent plane, then a small change in $x$
      is $dx=x-2$. What are $dy$ and $dz$?</li>

      <li>Explain why an equation of the tangent plane is

        <div class="marginpar">
          We'll construct a graph of $f$ and it's tangent plane i