\documentclass{standalone}
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\usepackage{tgchorus}
\usepackage[T1]{fontenc}
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\begin{document}

\vskip2cm

\begin{exa}[colbacktitle=blue!85]{Exercice 1}
    Dans $\mathscr{M}_2(\mathbb{R})$, on considère le sous-ensemble :

  \[
    E = \left\{M(x) = \begin{pmatrix}
        x & x \\
        0 & 0
    \end{pmatrix} \mid x \in \mathbb{R}\right\}, \text{ On pose : } E^* = E - \{M(0)\}
  \]
\end{exa}

\end{document}