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IMO 1969 - Longlist Problems Question 10

IMO Shortlist · IMO 1969 - Longlist Problems

Question 10

(BUL 4) Let $M$ be the point inside the right-angled triangle $ABC$ $(\angle C=90^\circ)$ such that
$$\angle MAB=\angle MBC=\angle MCA=\varphi.$$
Let $\psi$ be the acute angle between the medians of $AC$ and $BC$. Prove that $\frac{\sin(\varphi+\psi)}{\sin(\varphi-\psi)}=5$.