roach that is not a straight line.
  </div>
</section>
                <section>
  <h1>The Derivative</h1>
    <p>Before we introduce derivatives, let's
  recall the definition of a differential. If $y=f(x)$ is a
  function, then we say the differential $dy$ is the expression
  $dy=f'(x) dx$ (we could also write this as $dy =
  \frac{dy}{dx}dx$). Think of differential notation $dy=f'(x)dx$ in
  the following way:</p>

  <blockquote>
    A small change in the output $y$ equals the derivative
    multiplied b