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integer f(x) = x^4 +ax^3 +bx^2 +cx+d with exactly one real root

Source: Israel Grosman Memorial Mathematical Olympiad 1999 p4

February 15, 2020
Integer PolynomialpolynomialFactoringalgebra

Problem Statement

Consider a polynomial f(x)=x4+ax3+bx2+cx+df(x) = x^4 +ax^3 +bx^2 +cx+d with integer coefficients. Prove that if f(x)f(x) has exactly one real root, then it can be factored into nonconstant polynomials with rational coefficients