Construct the envelope formed by a fix diameter of a circle rolling along a fixed circle of the same size .

> restart;

> m:=[[2*cos(t)-cos(2*t),2*sin(t)-sin(2*t)],[2*cos(t)+cos(2*t),2*sin(t)+sin(2*t)]];

> t:=n*Pi/50;

> plot([m$n=0..100],axes=none,scaling=constrained,color=brown);

>