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~-~Relatif à l'exercice #1
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\begin{document}
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\chapHead{DNB 2014,\\
Amérique du Nord}

\section*{Exercice 1 (4 points)}

Cet exercice est un questionnaire à choix multiples (QCM). Pour chaque question, une seule réponse est exacte. Aucune justification n'est demandée.

\medskip

{\em Pour chacune des quatre questions, écrire sur votre copie le numéro de la question et la lettre A, B, ou C correspondant à la réponse choisie.}

\medskip

\begin{tabularx}{\linewidth}{|S{m{0.5\linewidth}}|*3{S{>{\centering\arraybackslash}X}|}}
\hline
& \textbf{A} & \textbf{B} & \textbf{C}\\
\hline
{\color{purple}1.}~$\left(\dfrac{2}{7}+\dfrac{3}{7}\right):\dfrac{1}{5}=$ & 
$\dfrac{1}{7}$ & $\dfrac{25}{7}$ & $\dfrac{17}{7}$\\
\hline
{\color{purple}2.}~Le PGCD des nombres 84 et 133 est ... & 1 & 7 & 3\\
\hline
{\color{purple}3.}~Les solutions de l'inéquation $-3x+5\geqslant9$ sont les nombres $x$ tels que ... & $x\leqslant\dfrac{-4}{3}$ & $x=\dfrac{-4}{3}$ & $x\geqslant\dfrac{-4}{3}$\\
\hline
{\color{purple}4.}~$\left(1+\sqrt{2}\right)^2$ est égal à ... & 3 & $3-\sqrt{2}$ & $3+2\sqrt{2}$\\
\hline
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\end{document}