/B {-3 -3} def
/A {-1 4} def
/C {4 0} def

%% les milieux
/J {B C milieu} def
/I {A B milieu} def

%% on marque les longueurs
B I 2 marked
I A 2 marked
B J 1 marked
J C 1 marked

1.7 setcurvelinewidth
[B A C] polygone

orange
.7 setcurvelinewidth
[J I] ligne

bleu
setTimesItalic
   (B) B dltext
   (A) A urtext
   (C) C drtext
   (J) J drtext
   (I) I ultext