k on really large
  problems. The other way requires that we parametrize the surface
  $z=f(x,y)$ as $\vec r(x,y)=(x,y,f(x,y))$ and then use the cross
  product on the partial derivatives. Both give the same answer.
  The next problem has you give a general formula for a tangent
  plane. To tackle this problem, you'll need to make sure you can
  use symbolic notation. The review problem should help with this.</p>

  <div class="review">
    Joe wants to to find the tangent line to $y=x^3$ at $x=2$. He
    k