%% auteur : gh
100 setxunit
-2.5 2.5 setxrange
-1.5 1.5 setyrange

/O {0 0} def
/a 2 def
/b 1 def
/c {a 2 exp b 2 exp sub sqrt} def
/F {c  0} def
/F' {c neg 0} def
/Dx {a 2 exp c div  0} def
/Dx' {a 2 exp c div neg 0} def
/D {Dx Dx 0 1 addv} def
/D' {Dx' Dx' 0 1 addv} def

/X {Cos a mul} def
/Y {Sin b mul} def

traceaxes
axesarrow
16 setfontsize
setTimesItalic
   (O) O dltext

2 setlinewidth
rouge
O F (-) line
O 0 b (-) line
F 0 b (-) line
F O 0 b angledroit

1 setlinewidth
noir
/dy {0 0.1} def
/dx {0.1 0} def
O dy subv F dy subv (<->) line
(c) O dy subv F dy subv milieu dctext
O dx subv 0 b dx subv (<->) line
(b) O dx subv 0 b dx subv milieu cltext
0 b dx dy addv addv F dx dy addv addv (<->) line
(a) 0 b dx dy addv addv F dx dy addv addv milieu urtext


1.2 setlinewidth
vert
0 pi 2 mul settrange
{X} {Y} courbeparam

1.2 setlinewidth
continu
bleu
[F F'] points
D droite
D' droite
setTimesItalic
(F) F dctext
(F') F' drtext
(D) Dx 0 1.5 subv urtext
(D') Dx' 0 1.5 subv urtext