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exists n f^(n)(x)=0 implies f is a polynomial if f is analytic

Source: VJIMC 2004 2.4

July 12, 2021
algebrapolynomialreal analysis

Problem Statement

Let f:RRf:\mathbb R\to\mathbb R be an infinitely differentiable function. Assume that for every xRx\in\mathbb R there is an nNn\in\mathbb N (depending on xx) such that f(n)(x)=0.f^{(n)}(x)=0.Prove that ff is a polynomial.