25 setxunit
7.5 setborder
-20 20 setxrange
-20 20 setyrange
/a 1 def
/b 4 def
/c 3 def
/resolution 1000 def
      
2 2 settkstep
1 1 setsubtkstep
2 2 setmkstep
yticks
traceaxes
axesarrow
unites
0.75 setlinewidth
continu
bleu
/X {settvar
#rpn#   (a*b) * Cos (t) *c * Sin (t*(1+a/b))+ Sin (t)
} def
/Y {settvar
#rpn#   (a*b) * Sin (t) *c * Cos(t/(1+a*b))+Cos (t) 
} def
  0  20 pi mul {X} {Y} Courbeparam