Isoceles Tetrahedron
Source: 1972 USAMO Problem 2
March 6, 2010
geometry3D geometrytetrahedroninequalitiesparallelogramtriangle inequality
Problem Statement
A given tetrahedron is isoceles, that is, AB\equal{}CD, AC\equal{}BD, AD\equal{}BC. Show that the faces of the tetrahedron are acute-angled triangles.