MathDB
silk road special polynomials, one subset with no real root, one with real roots

Source: SRMC 2007

September 2, 2018
algebrapolynomialReal Roots

Problem Statement

The set of polynomials f1,f2,,fnf_1, f_2, \ldots, f_n with real coefficients is called special , if for any different i,j,k{1,2,,n}i,j,k \in \{ 1,2, \ldots, n\} polynomial 23fi+fj+fk\dfrac{2}{3}f_i + f_j + f_k has no real roots, but for any different p,q,r,s{1,2,,n}p,q,r,s \in \{ 1,2, \ldots, n\} of a polynomial fp+fq+fr+fsf_p + f_q + f_r + f_s there is a real root. a) Give an example of a special set of four polynomials whose sum is not a zero polynomial. b) Is there a special set of five polynomials?