\documentclass[12pt,a4paper]{article}
\usepackage[francais]{babel}
\usepackage{mafr}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{lmodern}
\usepackage[dvipsnames]{xcolor}
\usepackage{pstricks}
\begin{document}
\begin{pspicture}(0,0)(4,3)
\pspolygon(1,1)(3,1)(3,2)%
\uput{3pt}[90]{0}(3,2){$A$}%
\uput{3pt}[180]{0}(1,1){$B$}%
\uput{3pt}[-45]{0}(3,1){$C$}%
\end{pspicture}
\end{document}
