MathDB
Finitely (many) numbers

Source: Italy National Olympiad 2020 P3

September 30, 2020
algebra

Problem Statement

Let a1,a2,,a2020a_1, a_2, \dots, a_{2020} and b1,b2,,b2020b_1, b_2, \dots, b_{2020} be real numbers(not necessarily distinct). Suppose that the set of positive integers nn for which the following equation: a1xb1+a2xb2++a2020xb2020=n|a_1|x-b_1|+a_2|x-b_2|+\dots+a_{2020}|x-b_{2020}||=n (1) has exactly two real solutions, is a finite set. Prove that the set of positive integers nn for which the equation (1) has at least one real solution, is also a finite set.