-2.5 5 setxrange
-0.5 3 setyrange
50 setxunit
50 setyunit

/A {0 0} def
/B {4 0} def
/C {1 2} def
/D {1 0} def


C D B angledroit
[A B C] polygone
gsave
pointilles
[C D] ligne
grestore
<latex>
$a$
</latex>
2.9 0.9 [1.8 dup] ultexlabel

<latex>
$b$
</latex>
0.15 1.1 [1.8 dup] crtexlabel

<latex>
$c$
</latex>
2.1 0.05 [1.8 dup] dctexlabel

(A) A [1.5 dup] dltext
(B) B [1.5 dup] drtext
(C) C [1.5 dup] uctext
(C') D [1.5 dup] dctext

<latex>
$\rm{Abb}.\,2\ \ \ a)$
</latex>
-0.5 0.8 [2.0 dup] ultexlabel