$. Replace $dx$, $dy$,
      and $f'(3)$ with what we know they equal, to obtain an
      equation $y-?=?(x-?)$. What line does this equation
      represent?</li>

      <li>Draw both $f$ and the equation from the previous part on
      the same axes.</li>
    </ol>
  </div>
    
    <p>In first semester calculus, differential notation says
  $dy=f' dx$. A small change in the inputs times the derivative
  gives the change in the outputs. For the next problem, the output
  is $z$, and input is $(x,y)$, whic