-5 3 setxrange
-4 7 setyrange

tracerepere
marks

/a -2 3 sqrt sub def
/b 3 sqrt -2 add def
/alpha -1 2 sqrt sub def
/beta 2 sqrt -1 add def

/f {
   dup		% x, x
   4 add	% x, x+4
   mul		% x^2+4x
   1 add
}  def

/g {1 add 2 mul} def

linewidth 1.5 mul setlinewidth
{f} courbe
{g} courbe

[-1 1 alpha beta] {dup f} apply dashpoints

setTimesItalic
%%    (O) O drtext
   (C) -4.5 dup f rtext
   (f) indice
   (C) 2 dup g rtext
   (g) indice
setSymbol
   (a) alpha 0 utext
   (b) beta 0 dtext