Skip to content / Đến nội dung
ThichHocToan.com

Hanoi Open Mathematics Competition 2016 Senior Question 11

HOMC · Hanoi Open Mathematics Competition 2016 Senior

Question 11

Let \(I\) be the incenter of triangle \(ABC\), and let \(\omega\) be its circumcircle. Line \(AI\) meets \(\omega\) again at \(D\ne A\). Let \(F\) and \(E\) lie on side \(BC\) and arc \(BDC\), respectively, such that \(\angle BAF=\angle CAE\lt \tfrac12\angle BAC\). Let \(X\) be the second intersection of line \(EI\) with \(\omega\), and let \(T\) be the intersection of segment \(DX\) with line \(AF\). Prove that \(TF\cdot AD=ID\cdot AT\).