Algebra · Polynomials · Integer coefficient polynomials · Integer roots · Divisibility

Problem 1, 2019

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NationalProof

Let

\[ P(x) = a_n x^n + \dots + a_1 x + a_0 \]

be a polynomial with integer coefficients. Suppose that \(P\) has two distinct integer zeros, neither of which is positive (\(P\) may have further zeros besides these two), and that \(P(1) = 2\). Prove that:

(a) \(a_0 = 0\);

(b) \(\displaystyle\sum_{2 \mid i} a_i = \sum_{2 \nmid i} a_i\), that is, the sum of the coefficients with even index equals the sum of the coefficients with odd index.

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Serbian National Competition (Drzavno takmicenje) 2019, high school grade I, category A, problem 1. Organized by the Mathematical Society of Serbia (DMS). Source