% Fichier exo4.12.tex - Ch. Rolland/O Reilly France
\documentclass{article}
\usepackage[latin1]{inputenc}
\begin{document}
$$
A = \left( \begin{array}{ccc}
             x-\lambda & 1         & 0 \\
             0         & x-\lambda & 1 \\
             0         & 0         & x-\lambda \\
           \end{array}
    \right)
$$
\end{document}
