Regular pentagon inscribed in a circle
Step 1. Draw a diameter of the circle, label the ends C and M
2. Construct a perpendicular to CM at O
3. Mark a point S where the bisector intersects the circle
4. Draw the perpendicular bisector of the segment SO, creating its midpoint L.
5. Draw a circle, center L, with radius LS
6. Draw a line from M through L, intersecting the small circle at N and P
7. With the compass on M, set its width to P
8. Draw a broad arc, crossing the given circle at A and E
9. With the compass on M, set its width to N
10. Draw a broad arc, crossing the given circle at B and D
11. Draw a line between each point A,B,C,D,E,A in turn
Done. The result is a regular pentagon ABCDE inscribed in the circle