MathDB
Square root sum approximation

Source: 2024 IRN-SGP-TWN Friendly Math Competition P3

August 2, 2024
algebra

Problem Statement

Let NN be a positive integer. Let RR denote the smallest positive number that is the sum of mm terms i=1m±ai\sum^m_{i=1}{\pm \sqrt{a_i}}, where each ai,i=1,,ma_i, i=1,\cdots, m is an integer not larger than NN. Prove that RCNm+32R\le C\cdot N^{-m+\frac{3}{2}} for some positive real number CC.
Proposed by Navid
(Clarification: note that the constant is allowed to depend on mm but should be independent of NN, i.e. the equation R(m,N)C(m)Nm+32R(m,N)\le C(m)\cdot N^{-m+\frac{3}{2}} should hold for all positive integers NN)