Question 117
Let $n \geqslant 3$ and let $x_{1}, \ldots, x_{n}$ be real numbers. Show that
$$
2\left(x_{1}+\cdots+x_{n}\right)^{2} \leqslant n\left(x_{1}^{2}+\cdots+x_{n}^{2}+x_{1} x_{2}+x_{2} x_{3}+\cdots+x_{n-1} x_{n}+x_{n} x_{1}\right)
$$
$$
2\left(x_{1}+\cdots+x_{n}\right)^{2} \leqslant n\left(x_{1}^{2}+\cdots+x_{n}^{2}+x_{1} x_{2}+x_{2} x_{3}+\cdots+x_{n-1} x_{n}+x_{n} x_{1}\right)
$$