Rational Solids with Equal Surface Area and Volume

Abstract

We classify pairs consisting of a right square pyramid and a right square prism, each having rational base side length and rational height, for which the two solids have equal surface area and equal volume. We prove that, up to scaling by a common positive rational factor, there is a unique such pair. The problem reduces to determining the rational points on a genus 2 bielliptic curve whose Jacobian has rank 2. We accomplish this using a quadratic Chabauty computation followed by the Mordell--Weil sieve. The same analysis gives an analogous classification for right circular cones and right circular cylinders.

10 pages