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IMO 2022 — Complete Shortlist Question 1

IMO Shortlist · IMO 2022 — Complete Shortlist

Question 1

Let $\left(a_{n}\right)_{n \geqslant 1}$ be a sequence of positive real numbers with the property that

$$
\left(a_{n+1}\right)^{2}+a_{n} a_{n+2} \leqslant a_{n}+a_{n+2}
$$

for all positive integers $n$. Show that $a_{2022} \leqslant 1$.