%% auteur : Florent Braisaz

-4.9 4.9 setxrange
-4.9 4.9 setyrange
15 setxunit
15 setyunit

gsave
1.25 setlinewidth
rouge

grestore

/A{-3 -3} def
/B{3 -1} def
/I{0 -2} def

/J{B I 90 rotatepoint} def
/K{I J 180 rotatepoint} def
/M{K J milieu} def


1.25 setlinewidth
[A B] ligne

gsave
bleu
pointilles
[M A] ligne
[M B] ligne
[M A M B]{2 marked} dapply
grestore

gsave
rouge
M I droite
[A I I B]{1 marked} dapply
B I M angledroit


#latex# ${\Delta}$ 
0.5 -3.5 [1.5 dup] crtexlabel
grestore

gsave
setTimesItalic
(A) A [1.5 1.5] cltext
(B) B [1.5 1.5] crtext
(I) I [1.5 1.5] dltext
(M) M [1.5 1.5] cltext
grestore