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IMO 1967 - Longlist Problems Question 4

IMO Shortlist · IMO 1967 - Longlist Problems

Question 4

(BUL 4) Suppose medians $m_a$ and $m_b$ of a triangle are orthogonal. Prove that:
(a) The medians of that triangle correspond to the sides of a right-angled triangle.
(b) The inequality $$5(a^2+b^2-c^2)\geq8ab$$ is valid, where $a,b,c$ are side lengths of the given triangle.