right angle wanted, incircle, circumcircle, perpendicular diagonals
Source: 2020 Croatia MO p3
February 16, 2021
geometryright angleperpendicular
Problem Statement
Given a triangle such that . On sides and , points and are marked respectively such that the lines and are perpendicular, and the circle inscribed in the triangle touches the length . The line intersects the circle circumscribed around the triangle at the points and . If the lines and intersect at one point, prove that the angle is right.