\documentclass[12pt]{article}
\usepackage[latin1]{inputenc}
\usepackage[french]{babel}
\usepackage{tikz}
\usetikzlibrary{arrows}
\usepackage{nopageno}
\parindent=0pt
\begin{document}

\begin{tikzpicture}[scale=0.5,>=stealth']
\draw[gray!50,dashed] (0,0) grid (29,24);
\begin{scope}[xshift=2cm,yshift=3cm]
\draw (0,0) rectangle +(13,13);
\draw (5,0) -- (5,13);
\draw (0,0) -- (5,13);
\draw (5,5) -- (13,8);
\draw[<->] (-1,0) -- (-1,13) node[midway,left] {13};
\draw[<->] (0,14) -- (5,14) node[midway,above] {5};
\draw[<->] (5,14) -- (13,14) node[midway,above,fill=white] {8};
\node[circle,draw,fill=white] at (2,9) {1};
\node[circle,draw,fill=white] at (3,3) {2};
\node[circle,draw,fill=white] at (9,9) {3};
\node[circle,draw,fill=white] at (9,3) {4};
\node[fill=white,draw,rounded corners] at (6.5,-2) {\bfseries Figure 1};
\end{scope}

\begin{scope}[xshift=20cm,yshift=2cm]
\draw (0,0) rectangle +(8,21);
\draw (8,0) -- (0,21);
\draw (0,8) -- (5,8);
\draw (8,13) -- (3,13);
\node[circle,draw,fill=white] at (2,11) {1};
\node[circle,draw,fill=white] at (6,10) {2};
\node[circle,draw,fill=white] at (3,4) {3};
\node[circle,draw,fill=white] at (5,17) {4};
\node[fill=white,draw,rounded corners] at (4,-1) {\bfseries Figure 2};
\end{scope}
\end{tikzpicture}

\bigskip

Nous avons découpé le carré de la Figure 1 afin de constituer la Figure 2.

\medskip

\begin{enumerate}
\item Calculer l'aire de la Figure 1.
\item Calculer l'aire de la Figure 2.
\item Que peut-on conclure ?
\item Expliquer ce dernier résultat.
\end{enumerate}
\end{document}