25 setxunit

-5 5 setxrange
-4 4 setyrange
1 1 settkstep
.5 .5 setsubtkstep
2 2 setmkstep
ticks
%marks
traceaxes
axesarrow
/f {setxvar
    1 x 2 exp sub sqrt
} def
/g {setxvar
    4 x 2 exp sub sqrt neg
} def
/ff {setxvar
   6 x 2 exp sub sqrt
} def
/gg {setxvar
    10 x 2 exp sub sqrt neg
} def
gsave
   noir
   1.75 setlinewidth
   continu
   1 neg 1 {f} Courbe
grestore
gsave
   noir
   1.75 setlinewidth
   continu
   2 neg 2 {g} Courbe
grestore
gsave
   noir
   1.75 setlinewidth
   continu
   2.449 2.449 neg {ff} Courbe
grestore
gsave
   noir
   1.75 setlinewidth
   continu
  3.162 3.162 neg  {gg} Courbe
grestore