Problem

Source: Brazilian Mathematical Olympiad 2024, Level 3, Problem 4

Tags: geometry, tangent



Let \( ABC \) be an acute-angled scalene triangle. Let \( D \) be a point on the interior of segment \( BC \), different from the foot of the altitude from \( A \). The tangents from \( A \) and \( B \) to the circumcircle of triangle \( ABD \) meet at \( O_1 \), and the tangents from \( A \) and \( C \) to the circumcircle of triangle \( ACD \) meet at \( O_2 \). Show that the circle centered at \( O_1 \) passing through \( A \), the circle centered at \( O_2 \) passing through \( A \), and the line \( BC \) have a common point.