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VMO 1976 — Division A Question 2

VMO · VMO 1976 — Division A

Question 2

Determine the shape of triangle $ABC$ knowing that
$$\frac{a\cos A+b\cos B+c\cos C}{a\sin A+b\sin B+c\sin C}=\frac{a+b+c}{9R},$$
where $a,b,c$ are the lengths of $BC,CA,AB$ and $R$ is the circumradius of triangle $ABC$.