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Polynomial with coefficients -1 or 1

Source: Kvant Magazine No. 9 2019 M2575

March 14, 2023
algebrapolynomialKvant

Problem Statement

Let t(1,2)t\in (1,2). Show that there exists a polynomial P(x)=anxn+an1xn1+...+a1x+a0P(x)=a_nx^n+a_{n-1}x^{n-1}+...+a_1x+a_0 with the coefficients in {1,1}\{1,-1\} such that P(t)20191.\left|P(t)-2019\right| \leqslant 1.
Proposed by N. Safaei (Iran)