-3 3 setxrange
-.5 3 setyrange
traceaxes
axesarrow
[-2 -1 1 2] {xmark} apply
1 ymark

/f {
   dup mul 1 sub sqrt
} def

/A1 {2 sqrt dup f} def
/B1 {2 sqrt neg dup f} def
/A2 {2 dup f} def
/B2 {-2 dup f} def
gsave
   pointilles
   [A1 projx A1 B1 B1 projx] ligne
   [A2 projx A2 B2 B2 projx] ligne
grestore

medium setlinewidth
-1 -3 {f} Courbe
1 3 {f} Courbe

setTimesItalic
   (O) O drtext
   (C) 2.5 dup f ultext
   (f) indice
   (x  ) xmax 0 ultext
   (y ) 0 ymax dltext