\begin{frame}
  \frametitle{Area Between Curves}

  \begin{block}{}
    The area between two curves $f(x)$ and $g(x)$ from $a$ to $b$ is:
    \begin{talign}
      A = \int_a^b |f(x) - g(x)|dx
    \end{talign} 
  \end{block}
  
  \begin{center}
  \scalebox{.8}{
  \begin{tikzpicture}[default,xscale=2]
    \def\mfuna{(cos (180/pi *\x))}
    \def\mfunb{(sin (180/pi *\x))}

    \diagram[1]{-.5}{3}{-1}{1.2}{1}
    \diagramannotatez
    \def\mfunshift{0}
    \begin{scope}[ultra thick]
      \draw[cred] plot[smooth,domain=-.5:3,samples=100] (\x,{\mfuna}) node[above] {$f(x)$};
      \draw[cblue] plot[smooth,domain=-.5:3,samples=100] (\x,{\mfunb}) node[above,yshift=1.5mm] {$g(x)$};
      \draw[fill=cgreen,draw=none,opacity=.5] plot[smooth,domain=.25:pi/4,samples=100] (\x,{\mfuna}) -- plot[smooth,domain=pi/4:.25,samples=100] (\x,{\mfunb}) -- cycle;
      \draw[fill=cgreen,draw=none,opacity=.5] plot[smooth,domain=pi/4:pi/2,samples=100] (\x,{\mfuna}) -- plot[smooth,domain=pi/2:pi/4,samples=100] (\x,{\mfunb}) -- cycle;
      \draw[gray] (.25,.1) -- node[at end,below,black] {$a$} (.25,-.1);
      \draw[gray] (pi/2,.1) -- node[at end,below,black] {$b$} (pi/2,-.1);
    \end{scope}
  \end{tikzpicture}
  }\\[1ex]
  \pause
  \alert{The area between $f$ and $g$ = area between $f-g$ and the $x$-axis.}\\[.2ex]
  \scalebox{.8}{
  \begin{tikzpicture}[default,xscale=2]
    \def\mfun{(cos (180/pi *\x) - sin (180/pi *\x))}

    \diagram[1]{-.5}{3}{-1}{1.2}{1}
    \diagramannotatez
    \def\mfunshift{0}
    \begin{scope}[ultra thick]
      \draw[cgreen] plot[smooth,domain=-.5:3,samples=100] (\x,{\mfun}) node[above] {$f(x)-g(x)$};
      \draw[fill=cgreen,draw=none,opacity=.5] plot[smooth,domain=.25:pi/2,samples=100] (\x,{\mfun}) -- (pi/2,0) -- (.25,0) -- cycle;
      \draw[gray] (.25,.1) -- node[at end,below,black] {$a$} (.25,-.1);
      \draw[gray] (pi/2,.1) -- node[at end,below,black] {$b$} (pi/2,-.1);
    \end{scope}
  \end{tikzpicture}
  }
  \end{center}
\end{frame}