Every school kid has been told that a circle of radius r has circumference=2\[pi] r. here is a parameterization of a circle of radius r: clear[x, y,t, r]; {x[t_],y[t_]}={r cos[t],r sin[t]}{r cos[t],r sin[t]}to get the whole circle, you run t from 0 to 2\[pi].use this information to confirm that the circumference of a circle of radius r measures out to 2\[pi] r units long.