25 setxunit
7.5 setborder
-6 6 setxrange
-6 6 setyrange
jpegmode
/a 5 def
/b 7 def
/c 2.2 def

2 2 settkstep
1 1 setsubtkstep
2 2 setmkstep
ticks
traceaxes
axesarrow
.75 setlinewidth
continu
bleu
/X {settvar
    a b sub t Cos mul c t 1 neg a b div add mul Cos mul add
} def
/Y {settvar
    a b sub t Sin mul c t 1 neg a b div add mul Sin mul sub
} def
  0  15 pi mul {X} {Y} Courbeparam