size(0,150); pair z0=0; pair z1=1; real theta=30; pair z=dir(theta); draw(circle(z0,1)); filldraw(z0--arc(z0,1,0,theta)--cycle,lightgrey); dot(z0); dot(Label,z1); dot("$(x,y)=(\cos\theta,\sin\theta)$",z); arrow("area $\frac{\theta}{2}$",dir(0.5*theta),2E); draw("$\theta$",arc(z0,0.7,0,theta),LeftSide,Arrow,PenMargin);