quadrillage
%160 setheight
%160 setwidth

10 setfontsize

-.5 2 setxrange
-.5 1.5 setyrange

traceaxes
unites

/D {1.5 .75 -1 1.6} def

O D orthoproj /H defpoint                              %% projete orthogonal de O sur D
/d {H dup mul exch dup mul add sqrt 1 exch div} def    %% 1/OH
/H' {d dup mul O H ABpoint} def
O H D popp angledroit

D droite
H' times2
O H' diamcercle cercle

/D' {1.3 0 1.3 3} def
O D' orthoproj /A defpoint                              %% projete orthogonal de O sur D
/d {A dup mul exch dup mul add sqrt 1 exch div} def    %% 1/OA
/A' {d dup mul O A ABpoint} def

D' droite
A' times2
A times2
O A' diamcercle cercle

pointilles
[O H] ligne
/dotscale {1.3 dup} def
O circ

setTimesItalic
   (O) O dltext
   ( H') H' rtext
   (H ) H dltext
   ( A') A' urtext
   (A ) A urtext
   (D) 1.7 .7 text
   (x=a) D' popp pop -.5 rtext
   (C) -.3 .7 rtext
setTimes
   (1) indice
setTimesItalic
   (C)  .7 -.3 text
setTimes
   (2) indice