\frametitle{Newton's Method}
    \begin{scope}[ultra thick]
      \draw[cgreen,ultra thick] plot[smooth,domain=-0:3.3,samples=200] function{-.5 + (.5*x)**3};
      \node[include=cgreen] (r) at (1.58,0) {};
      \node[anchor=south east] at (r) {$r$};
      \draw[gray] (3.2,-.2) -- node[at start,below,black] {$x_1$} node[include=cred,at end] {} (3.2,{-.5 + (.5*3.2)^3});
      \tangent{4cm}{.5cm}{-.5 + (.5*\x)^3}{3.2}
      \draw[gray] (2.28,-.2) -- node[at start,below,xshift=1mm,black] {$x_2$} (2.28,.2);

  \begin{exampleblock}{Idea of Newton's Method}
      \item Take an approximation $x_1$ of the root (a rough guess).
      \item Compute the tangent $L_1$ at $(x_1,f(x_1))$.
      \item The tangent $L_1$ is close to the curve\ldots
        so $x$-intercept of $L_1$ will be close the the $x$-intercept of the function.
  We can repeat this procedure to get improve the approximation.