Problem

Source: Olimphíada 2023 - Problem 1/Level U

Tags: floor function, algebra, inequalities, college contests



Let $n \geq 2023$ be an integer. For each real $x$, we say that $\lfloor x \rceil$ is the closest integer to $x$, and if there are two closest integers then it is the greater of the two. Suppose there is a positive real $a$ such that $$\lfloor an \rceil = n + \bigg\lfloor\frac{n}{a} \bigg\rceil.$$Show that $|a^2 - a - 1| < \frac{n\varphi+1}{n^2}$.