%% auteur : gh

200 setxunit
-1 1 setxrange
-1 1 setyrange

traceaxes
axesarrow

/O {0 0} def
16 setfontsize
setTimesItalic
   (O) O dltext

/rho {3 mul Sin} def
/rho' {3 mul Cos 3 mul} def

/X {dup rho exch Cos mul} def
/Y {dup rho exch Sin mul} def

/X' {settvar t rho' t Cos mul t rho t Sin mul sub} def
/Y' {settvar t rho' t Sin mul t rho t Cos mul add} def

orange
1 setcurvelinewidth
pi 6 div pi 2 mul settrange
{X} {Y} courbeparam

1.7 setcurvelinewidth
rouge
0 pi 6 div settrange
{X} {Y} courbeparam

bleu
1 setcurvelinewidth
0.4 settailletangente
0 (X)(Y) ptangente 
pi 6 div (X)(Y) ptangente 

noir
<tex>
$$ M(0) $$
</tex>
0 X 0 Y [1.3 1.3] drtexlabel
<tex>
$$ M(\pi /6) $$
</tex>
pi 6 div X pi 6 div Y [1.3 1.3] dltexlabel
<tex>