\begin{exercice*}
  On consid\`{e}re la fonction $u$ d\'{e}finie sur $\R$ par~:
  $u\left(x\right)=x^2-1$.

  Associer chacune des fonctions $u$, $-u$, $u+2$ et $-\dfrac{1}{4}u$
  \`{a} sa courbe repr\'{e}sentative.

  {\centering
    \begin{tikzpicture}[general,x=.5cm,y=.5cm]
    \draw [quadrillage,step=.5cm] (-3,-3) grid (3,5);
    \draw [axe] (-3,0) -- (3,0);
    \draw [axe] (0,-3) -- (0,5);
    \node (O) at (0,0) [below right] {0};
    \draw (2,0) node {+} [below] node {2};
    \draw (0,2) node {+} [left] node {2};

    % u
    \draw [J1,smooth] plot [domain=-2.25:2.25] (\x,{abs(\x^2) - 1});
    % -u
    \draw [G1,smooth] plot [domain=-2:2] (\x,{abs(\x^2) + 1});
    % u + 2 ?
    \draw [F1,smooth] (-3,-2) parabola bend (0,.25) (3,-2);
    % -1/4u
    \draw [A1,smooth] plot [domain=-2:2] (\x,{-abs(\x^2) + 4 / 4});
  \end{tikzpicture}
  \par}
\end{exercice*}
\begin{corrige}
  $u$, $-u$, $u+2$ et $-\dfrac{1}{4}u$ ont pour repr\'{e}sentations
  graphiques respectives $C_{2}$, $C_{1}$, $C_{4}$ et $C_{3}$.
\end{corrige}