\newcommand{\sys4}[5] {
\ifthenelse{\equal{#1}{}}{ %vide premier parametre systeme normal
        \left\{
            \begin{array}{l}
                #2 \\
                #3 \\
                #4 \\
                #5
            \end{array}
        \right.
}{
            \begin{array}{rl}
                ~ & #2 \\
                #1 & #3 \\
                #1 & #4 \\
                #1 & #5
            \end{array}
}}
\newcommand{\sys3}[4] {
\ifthenelse{\equal{#1}{}}{ %vide premier parametre systeme normal
        \left\{
            \begin{array}{l}
                #2 \\
                #3 \\
                #4
            \end{array}
        \right.
}{
            \begin{array}{rl}
                ~ & #2 \\
                #1 & #3 \\
                #1 & #4
            \end{array}
}}
\newcommand{\sys2}[3] {
\ifthenelse{\equal{#1}{}}{ %vide premier parametre systeme normal
        \left\{
            \begin{array}{l}
                #2 \\
                #3
            \end{array}
        \right.
}{
            \begin{array}{rl}
                ~ & #2 \\
                #1 & #3
            \end{array}
}}