system with parameter $m$

Question

\documentclass[12pt,a4paper]{article}
%------------------------------------------------------------
\usepackage{amsmath,amssymb,amsthm,mathdots}
\begin{document}
Soit $m$ un nombre r\'eel. On consid\`ere le syst\`eme lin\'eaire suivant:
\begin{equation*}
(S):\left\{
      \begin{aligned}
-2y+z &=1 \\
mx- 3y+mz &=0\\
mx-2y &=2
          \end{aligned}
           \right.
\end{equation*}
\end{document} 

Is there a nicer way to write it?

Answer 1

You're using the systeme tag: that's about the systeme package (documentation in French).

\documentclass[12pt,a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage[french]{babel}
\usepackage{amsmath,amssymb,amsthm,mathdots}
\usepackage{systeme}

\begin{document}

Soit $m$ un nombre réel. On considère le système linéaire suivant:
\begin{equation*}
(S):
\systeme[xyz]{
  -2y+z = 1,
  mx- 3y+mz = 0,
mx-2y = 2
}
\end{equation*}

\end{document}

Since we want that m is considered as a parameter, we need to tell explicitly what the unknowns are.

Direct input of accented letters has worked for a long time.

If you prefer left alignment, you were almost on the right track.

\documentclass[12pt,a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage[french]{babel}
\usepackage{amsmath,amssymb,amsthm,mathdots}

\begin{document}

Soit $m$ un nombre réel. On considère le système linéaire suivant:
\begin{equation*}
(S):
\left\{
  \begin{aligned}
  & {-}2y+z = 1 \\
  & mx- 3y+mz = 0 \\
  & mx-2y = 2
  \end{aligned}
\right.
\end{equation*}

\end{document}

Note {-} in order to make it a unary symbol rather than an operation symbol.