function y=regPolygon(n)
R=1;
t=0:0.01:2*pi;
x=R*cos(t);
y=R*sin(t);
m=linspace(pi/2,5/2*pi,n+1);
xz=R*cos(m);
yz=R*sin(m);
hold on
plot(x,y,xz,yz);
axis equal;