MathDB
Bounds on degree of polynomials

Source: 2020 Israel Olympic Revenge P3

June 11, 2022
number theoryPolynomialsolympic revengealgebrapolynomial

Problem Statement

For each positive integer nn, define f(n)f(n) to be the least positive integer for which the following holds:
For any partition of {1,2,,n}\{1,2,\dots, n\} into k>1k>1 disjoint subsets A1,,AkA_1, \dots, A_k, all of the same size, let Pi(x)=aAi(xa)P_i(x)=\prod_{a\in A_i}(x-a). Then there exist iji\neq j for which deg(Pi(x)Pj(x))nkf(n)\deg(P_i(x)-P_j(x))\geq \frac{n}{k}-f(n)
a) Prove that there is a constant cc so that f(n)cnf(n)\le c\cdot \sqrt{n} for all nn.
b) Prove that for infinitely many nn, one has f(n)ln(n)f(n)\ge \ln(n).