Let $\triangle ABC$ with incenter $I$. Two points $D$, $E$ lie on the line $BC$ such that $(E,D;B,C)=-1$. Let $F$ be the projection of $D$ onto $IE$. Prove that $\angle AFI=\angle IDC$.
2026-03-30 14:01:03.1774879263
Harmonic points and equal angles
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