autocrop
-10 8 setxrange
-5 7 setyrange

/A {0 0} def
/B {0 4.5} def
/C {-9 3 sqrt mul 2 div 0} def

[A B C] polygone
C A B angledroit

C B A 1.2 (-) tripointarc

setTimesItalic
   (A) A drtext
   (B) B urtext
   (C) C dltext
setTimes
   (60°) -120 B 1.2 cpoint dltext

<tex>
$$
   {2\sqrt 3}
$$
</tex>

A B milieu [1.3 dup] crtexlabel