\begin{methode}[Construire la somme de deux vecteurs \MethodeRefExercice*{2G3_E_construire_somme}]\label{2G3_M_construire_somme}
On remplace l'un des deux vecteurs par un représentant: 
\begin{itemize}
\item soit de même origine afin d'utiliser la règle du parallélogramme;
\item soit d'origine l'extrémité de l'autre afin d'utiliser la relation de Chasles.
\end{itemize}
\exercice[0.3]
\vspace{-0.5em}
\begin{enumerate}
\item  Construire un carré $ABCD$ de centre $O$.
\item Construire les vecteurs \par
$\vv u=\vv{AB}+\vv{OD}$ et 

$\vv v=\vv{AD}+\vv{OC}$
\end{enumerate}
\correction
\hfill
\begin{tikzpicture}[general]
  \draw (0,0) node[below] {$A$};
  \draw (2,0) node[below] {$B$};
  \draw (2,2) node[above] {$C$};
  \draw (0,2) node[above] {$D$};
  \draw (1,1) node[right] {$O$};
  \draw[color=B1] (0.5,0.5) node[above] {{\boldmath $\vv u$}};
  \draw (1,-1) node {Avec la relation};
  \draw (1,-1.5) node {de Chasles};
  \draw (1,3) node[below, white] {$A$};
\draw (0,0)--(2,0)--(2,2)--(0,2)--cycle;
\draw (0,0)--(2,2);
 \draw[->, color=A1, epais] (0,0)--(2,0);
 \draw[->, color=A1, epais] (1,1)--(0,2);
 \draw[->, color=A1, epais, dashed, line cap=butt] (2,0)--(1,1);
 \draw[->, color=B1, epais, line cap=butt] (0,0)--(1,1);
\end{tikzpicture} 
\hfill
\begin{tikzpicture}[general]
  \draw (0,0) node[below] {$A$};
  \draw (2,0) node[below] {$B$};
  \draw (2,2) node[above] {$C$};
  \draw (0,2) node[above] {$D$};
  \draw (1,1) node[right] {$O$};
\draw (0,0)--(2,0)--(2,2)--(0,2)--cycle;
\draw[dashed] (1,1)--(1,3)--(0,2);
\draw (0,2)--(2,0);
\draw[->, color=A1, epais] (0,0)--(0,2);
\draw[->, color=A1, epais, line cap=butt] (1,1)--(2,2);
\draw[->, color=A1, epais, dashed] (0,0)--(1,1);
\draw[->, color=B1, epais] (0,0)--(1,3);
\draw[color=B1] (1,3) node[right] {$\vv v$};
\draw (1,-1) node {Avec la règle};
\draw (1,-1.5) node { du parallélogramme};
\end{tikzpicture} 
\end{methode}
