IMC 2008 ziua 2 problema 4

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Beniamin Bogosel
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IMC 2008 ziua 2 problema 4

Post by Beniamin Bogosel »

Fie \( f,g \in \mathbb{Z}[X] \) neconstante astfel incat \( g | f \) in \( \mathbb{Z}[X] \). Demonstrati ca daca polinomul \( f-2008 \) are cel putin 81 de radacini intregi, atunci gradul lui \( g \) este mai mare decat 5.

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Beniamin Bogosel
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Post by Beniamin Bogosel »

Scriem \( f=gh \) cu \( h \in \mathbb{Z}[X] \) si astfel exista \( x_1,...,x_{81} \) astfel incat \( g(x_i)|2008,\ i=1,..,81 \). Cum 2008 are 16 divizori intregi, exista sase dintre \( x_i \) astfel incat \( g \) ia aceeasi valoare pentru fiecare dintre ei. Daca \( g \) nu ar avea gradul mai mare decat 5, ar fi constant. Contradictie.
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That's why it's called present. :)

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