all flat angles in pyramid at any vertex are either acute, or right, or obtuse
Source: I All-Ukrainian Tournament of Young Mathematicians, Qualifying p5
May 12, 2021
geometry3D geometrypyramidanglesUkrainian TYM
Problem Statement
The heights of a triangular pyramid intersect at one point. Prove that all flat angles at any vertex of the surface are either acute, or right, or obtuse.