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IMO 2017 — Complete Shortlist Question 1

IMO Shortlist · IMO 2017 — Complete Shortlist

Question 1

Let $a_{1}, a_{2}, \ldots, a_{n}, k$, and $M$ be positive integers such that

$$
\frac{1}{a_{1}}+\frac{1}{a_{2}}+\cdots+\frac{1}{a_{n}}=k \quad \text { and } \quad a_{1} a_{2} \ldots a_{n}=M
$$

If $M\gt 1$, prove that the polynomial

$$
P(x)=M(x+1)^{k}-\left(x+a_{1}\right)\left(x+a_{2}\right) \cdots\left(x+a_{n}\right)
$$

has no positive roots.