25 setxunit
7.5 setborder
-15 15 setxrange
-15 15 setyrange
jpegmode
/a 8 def
/b 6 def
/c 1 def
/resolution 500 def
      
2 2 settkstep
1 1 setsubtkstep
2 2 setmkstep
ticks
traceaxes
axesarrow
unites
0.75 setlinewidth
continu
bleu
/X {settvar
#rpn#   (a+b) * Cos (t) - c * Cos (t*(1+a/b))
} def
/Y {settvar
#rpn#   (a+b) * Sin (t) - c * Sin (t*(1+a/b))
} def
  0  20 pi mul {X} {Y} Courbeparam