MathDB
Parabolas passing through pairs of points

Source: St Petersburg 2021 9.4

December 23, 2021
algebra

Problem Statement

Given are nn points with different abscissas in the plane. Through every pair points is drawn a parabola - a graph of a square trinomial with leading coefficient equal to 11. A parabola is called goodgood if there are no other marked points on it, except for the two through which it is drawn, and there are no marked points above it (i.e. inside it). What is the greatest number of goodgood parabolas?