2018 homc The center of a circle and nine randomly selected points on this circle are colored in red. Every pair of those points is connected by a line segment, and every point of intersection of two line segments inside the circle is colored in red. What is the largest possible number of red points?

Respuesta :

Answer:

Max possible red points  = 220

Step-by-step explanation:

- Remark that a convex quadrilateral has exactly one intersection which is the intersection of its two diagonals.

- Consider 9 points on the circle, which give at most ( combination ):

                            [tex]\frac{9!}{4!5!} = 126[/tex] intersections.

- Now consider the center and the three points on the circle, there are at most ( combinations ):

                           [tex]\frac{9!}{3!6!} = 84[/tex] intersections.

- So the total number of red points would be:

                           Given = 10

                           2 Diagonals = 126

                           Center + 3 pts = 84

                         ======================

            Max possible red points  = 220

                         ======================