Source
20 setxunit
7.5 setborder
90 setangle_repere
-6 5 setxrange
-5 5 setyrange
1 1 settkstep
.5 .5 setsubtkstep
2 2 setmkstep
ticks
subticks
marks
traceaxes
axesarrow
unites
/f {setxvar
   x 1 add x x mul 2 x mul add 3 sub div
} def
gsave
   noir
   1.75 setlinewidth
   continu
  xmin  -3.1 {f} Courbe
  -2.9 0.9 {f} Courbe
  1.1 xmax {f} Courbe
grestore
gsave
   rouge
   .75 setlinewidth
   pointilles
-3 -1 -3 1 droite
1 -1 1 1 droite
grestore