The sum of the cosines of the flat angles of the trihedral angle is $-1$. Find the sum of its dihedral angles.
Problem
Source: 2019 Oral Moscow Geometry Olympiad grades 10-11 p6
Tags: geometry, 3D geometry, angles, solid geometry
Source: 2019 Oral Moscow Geometry Olympiad grades 10-11 p6
Tags: geometry, 3D geometry, angles, solid geometry
The sum of the cosines of the flat angles of the trihedral angle is $-1$. Find the sum of its dihedral angles.