Mardi 4 octobre
\left \{
\begin{array}{l}
2x - y = 5 \\\\
5x - 3y = 5
\end{array}
\right.
\left \{
\begin{array}{l}
x + y + z = 30 \\\\
x - y + z = 10 \\\\
x + y - z = 0
\end{array}
\right.
\left \{
\begin{array}{l}
x + 2y - z = 6 \\\\
x + y + z = 12 \\\\
-x + y + 2z = 11
\end{array}
\right.