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No consecutive zero coefficients

Source: XIII Ibero American Olympiad For University Students

July 22, 2011
algebrapolynomialinductionstrong inductionalgebra proposed

Problem Statement

Let p(x)=xn+an1xn1++a1x+a0p(x)=x^n+a_{n-1}x^{n-1}+\cdots+a_1x+a_0 be a monic polynomial of degree n>2n>2, with real coefficients and all its roots real and different from zero. Prove that for all k=0,1,2,,n2k=0,1,2,\cdots,n-2, at least one of the coefficients ak,ak+1a_k,a_{k+1} is different from zero.