2021 IMO Shortlist A7

Let $n \geq 1$ be an integer, and let $x_{0}, x_{1}, \ldots, x_{n+1}$ be $n+2$ non-negative real numbers that satisfy $x_{i} x_{i+1}-x_{i-1}^{2} \geq 1$ for all $i=1,2, \ldots, n$. Show that $$x_{0}+x_{1}+\cdots+x_{n}+x_{n+1}>\left(\frac{2 n}{3}\right)^{3 / 2}$$

设 $n \geq 1$ 为整数，并令 $x_{0}, x_{1}, \ldots, x_{n+1}$ 为 $n+2$ 个非负实数，对于所有 $i=1,2, \ldots, n$ 满足 $x_{i} x_{i+1}-x_{i-1}^{2} \geq 1$。证明 $$x_{0}+x_{1}+\cdots+x_{n}+x_{n+1}>\left(\frac{2 n}{3}\right)^{3 / 2}$$