MathDB
JBMO Shortlist 2023 G3

Source: JBMO Shortlist 2023, G3

June 28, 2024
JBMOJBMO Shortlistgeometrycircumcircletangent circles

Problem Statement

Let A,B,C,DA,B,C,D and EE be five points lying in this order on a circle, such that AD=BCAD=BC. The lines ADAD and BCBC meet at a point FF. The circumcircles of the triangles CEFCEF and ABFABF meet again at the point PP.
Prove that the circumcircles of triangles BDFBDF and BEPBEP are tangent to each other.