code for figure

> circ:=plot([cos(t),sin(t),t=0..2*Pi],thickness=3,
color=blue, xtickmarks=[],ytickmarks=[]):
rad:=plot([[0,0],[cos(Pi/3.),sin(Pi/3.)]], thickness=3,color=tan):
dotline:=plot([[cos(Pi/3.),0],[cos(Pi/3.),sin(Pi/3.)]],
thickness=3,color=black,linestyle=3):
txt:=plots[textplot]({[2*cos(Pi/3.),1.2*sin(Pi/3.),
`( x(theta), y(theta) )`
],[.25,.07,`theta`],[1.1,.1,`r`]},font=[TIMES,BOLD,14]):
plots[display]({txt,rad,dotline,circ},scaling=constrained);