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ASU 496 All Soviet Union MO 1989 a^2+b^2 +c^2 +4abc < 1/2, perimeter 1 triangle

Source:

August 13, 2019
geometryperimetergeometric inequalityinequalities

Problem Statement

A triangle with perimeter 11 has side lengths a,b,ca, b, c. Show that a2+b2+c2+4abc<12a^2 + b^2 + c^2 + 4abc <\frac 12.