\begin{questions}
      \item  Pour $P_{1}$, on a $\Delta=9-4\times(-2)\times5=49$,
        d'où :
        \[\left\{\begin{aligned}
         x_{1}& = \frac{-3+7}{-4} = -1\\
         x_{2}& =\frac{-3-7}{-4} = \frac{5}{2}
        \end{aligned}\right. \qquad S = \left\{ -1~;\frac{5}{2} \right\}\,.\]
      \item  Pour $P_{2}$, on a $\Delta=400-4 \times (-3) \times 7=484$,
        d'où :
        \[\left\{\begin{aligned}
        x_{1}& = \frac{-20+22}{-6} = -\frac{1}{3}\\
        x_{2}& = \frac{-20-22}{-6} = 7
        \end{aligned}\right. \qquad S = \left\{ -\frac{1}{3}~;7 \right\}\,.\]
\end{questions}
