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Tetrahedron

Source: St Petersburg Olympiad 2008, Grade 11, P5

August 30, 2017
geometry3D geometrytetrahedron

Problem Statement

All faces of the tetrahedron ABCDABCD are acute-angled triangles.AKAK and ALAL -are altitudes in faces ABCABC and ABDABD. Points C,D,K,LC,D,K,L lies on circle. Prove, that AB⊥CDAB \perp CD
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