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congruent faces in tetrahedron criterion

Source: Polish MO Recond Round 1987 p2

September 9, 2024
geometry3D geometrycongruent trianglestetrahedron

Problem Statement

Prove that the sum of the plane angles at each of the vertices of a given tetrahedron is 180∘ 180^{\circ} if and only if all its faces are congruent.