code for diagram

> grph:=plot([theta - .5*sin(theta),1-.5*cos(theta), theta=0..3*Pi],thickness=3,xtickmarks=[],ytickmarks=[],scaling=constrained,view=[-1..10,-.5..2]):
txt:=plots[textplot]({[-.3,1,`r`],[-.3,2,`2r`],[Pi,-.3,`Pi r`],[2*Pi,-.3,`2 Pi r`],[3*Pi,-.3,`3 Pi r`] },font=[TIMES,BOLD,14]):
plots[display]({grph,txt});