-3 6 setxrange
tracerepere
marks

/f {
   setxvar
   x dup mul 
   x 4 mul sub
   1 sub
} def

1.6 setlinewidth
{f} courbe

mixte
1 setlinewidth
{pop 2} courbe
{pop -1} courbe

1 -4 -3 solve2nddegre
2 dashpoint
2 dashpoint
4 -1 dashpoint