MathDB
Reflection about diagonal in harmonic quad

Source: Sharygin 2022

March 4, 2022
geometrygeometric transformationreflection

Problem Statement

The products of the opposite sidelengths of a cyclic quadrilateral ABCDABCD are equal. Let BB' be the reflection of BB about ACAC. Prove that the circle passing through A,B,DA,B', D touches ACAC