2023 WSMO Team Round Problems/Problem 12

Problem

Consider parabola $\mathcal P$ pointing upwards with vertex at the origin of the Cartesian plane. Denote the focus of it as $F$ and the directrix of it as $\mathcal L$. Point $P$ with $x$-coordinate $4$ is selected in $\mathcal P$. The perpendicular bisector of $FP$ meets $\mathcal L$ at $Q$. Given the $x$-coordinate of $Q$ is $3$, then $FP^2 = \frac{m}{n},$ for relatively prime positive integers $m$ and $n.$ Find $m+n.$

Solution