Stage: 5 Challenge Level: 
Prove that in every tetrahedron there is a vertex such that the three edges meeting there have lengths which could be the sides of a triangle.
Number theory. Stage 5 - Reviewed 2012. Inequality/inequalities. Manipulating algebraic expressions/formulae. alphas. epsilons. Dynamical systems. Tetrahedra. Proof by contradiction. Mathematical reasoning & proof.
Published November 2002,December 2002.
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