-2.5 5.5 setxrange
-0.5 3 setyrange
50 setxunit
50 setyunit

/A {0 0} def
/B {5 0} def
/M {2.143 0} def

/c {A B diamcercle} def
106.26 c cpoint /C defpoint
/P {M B C orthoproj} def
/Q {M A C orthoproj} def

[A B C] polygone
[C Q M P] polygone
A C B angledroit
/fillstyle {.5 setgray continu hachure} def
[C Q M P] polygone* 

(A) A [1.5 dup] dltext
(B) B [1.5 dup] drtext
(C) C [1.5 dup] uctext
(P) P [1.5 dup] urtext
(Q) Q [1.5 dup] ultext
(R) M [1.5 dup] dctext
<latex>
$x$
</latex>
1.2 0.7 [1.8 dup] dctexlabel

<latex>
$x$
</latex>
2.9 0.9 [1.8 dup] dctexlabel


<latex>
$\rm{Abb}.\,4\ \ a)$
</latex>
-0.4 1.1 [2.0 dup] ultexlabel