\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}
\usepackage{pst-eucl}
\begin{document}
\begin{footnotesize}
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\pspolygon(A)(B)(C)%
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\pstMiddleAB[PointName=M_{AC}]{A}{C}{M2}%
\pstMiddleAB[PointName=M_{BC},PosAngle=-10,PointNameSep=1.4em]{B}{C}{M3}%
\pcline[linestyle=dashed,linecolor=cyan](C)(M1)%
\pcline[linestyle=dashed,linecolor=cyan](B)(M2)%
\pcline[linestyle=dashed,linecolor=cyan](A)(M3)%
\pstCGravABC[PointSymbol=square*,linecolor=red]{A}{B}{C}{G}%
\end{pspicture}
\end{footnotesize}
\end{document}
