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MathNet 2025-part-01 — 187 problems (EN–VI) Question 147

Math Olympiad Vault · MathNet 2025-part-01 — 187 problems (EN–VI)

Question 147

In triangle $ABC$, the internal angle bisectors $BE$ and $CF$ intersect at point $I$. Let $F \in AB$, $E \in AC$. Let $D$ be the foot of the perpendicular from $I$ to $BC$. If $\angle A = 60^\circ$, prove that
$$
S_{BCF} + S_{BCE} = 3S_{BIC},
$$
where $S_{XYZ}$ denotes the area of triangle $XYZ$.
(Bilegdemberel Bat-Amgalan)