\documentclass[a4paper,12pt]{classPres}
\usepackage{tkz-fct}

\author{}
\title{}
\date{}

\begin{document}
\begin{frame}{Questions flashs}
    Développer l'expression
    \[ A = -3(x+5)^2 - 7 \]
    Mettre sous forme canonique
    \[ B = x^2 - 6x - 7 \]
\end{frame}

\begin{frame}{Correction}
    \begin{eqnarray*}
        A &=& -3(x+5)^2 - 7 \\
          &=& -3x^2 - 30x - 82 
    \end{eqnarray*}
    \hline
    \begin{eqnarray*}
       B = x^2 - 6x - 7
    \end{eqnarray*}
    \[ \alpha = \frac{-b}{2a} = 3 \]
    \[ \beta = -\frac{b^2-4ac}{4a} = -\frac{36+38}{4} = -16 \]
    \begin{eqnarray*}
        B &=& (x - 3)^2 - 16 \\
    \end{eqnarray*}
\end{frame}

\end{document}