Given a positive integer , does there exist a planar polygon and a point in its plane such that every line through that point meets the boundary of the polygon at exactly points?
Solution
The answer is in the affirmative. To describe the configuration, fix a coordinate frame and let be real numbers such that , and . Setting and , , the polygon and the origin satisfy the condition in the statement: the x-axis (respectively, y-axis) contains all vertices of odd (respectively, even) rank and no other points on the boundary; and every line through the first and third (respectively, second and fourth) quadrants crosses the sides and (respectively, and ), , and no other side, since the remaining sides all lie in the other two quadrants.
Want a route through all this instead of an archive? The track
puts 2,000 problems in a working order, from AMC 10 level to the IMO shortlist.