Maths Olympiad Prep

Library / /54 of 299

Geometry Difficulty 5.8 AIME, harder Prove it Iran

Give nn black points on the plane such that no three are collinear and the distance between any two of them are pairs distinct. Starting with an arbitrary point and make it red. At each step, we draw the smallest segment such that one of its endpoints is red and the other is black—that has not yet been drawn—and doesn't cut any other yet drawn segments. Then, we make its black endpoint red. Is it true that for any nn and for any formation of these nn points, after finitely many steps, we can make all the points red?

Solution

The answer is negative. We shall provide the following formations.

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.

Source: MathNet, licensed CC-BY-4.0. Statement reproduced verbatim; metadata (topic, difficulty) added by this project.