- Start with a (green) circle centered on A with radius AB. Point B is on this circle.
- Construct a line which intersects line AB at point A, in such a way that these two lines are perpendicular.
- This green circle intersects the newest line at two points. Designate one of these intersections as point C.
- Bisect segment AC, and mark point D as this segment’s midpoint.
- Construct a circle (the blue one) which is centered on D and includes point B.
- The blue circle intersects line AC at two points. Only one of these points is inside the green circle. Label this point F.
- Construct segment BF. This segment’s length is the edge length of the pentagon under construction.
- Construct a circle (the red one) which is centered on B and includes point F.
- The red and green circles have two points of intersection. One of them is closer to point F than the other; label this closer intersection as point I. The other point of intersection is closer to point C; label it J.
- J, B, and I are vertices of a regular pentagon. Construct a circle (orange) which is centered on point I and passes through point B. The orange and green circles intersect at two points, one of which is labeled B. Label the other one K. Point K is a vertex of the pentagon under construction.
- Construct a (purple) circle centered on K and passing through I. This purple circle intersects the green circle at two points, one of which is already labeled I. Label the other point of intersection as L. Point L is the fifth vertex of the pentagon.
- Connect points with segments to form regular pentagon JBIKL.
- Connect points with segments to form regular star pentagon BKJIL.
RobertLovesPi.net 