MathDB

concyclic wanted, excenter related

Source: TOT 363 1993 Spring A J2 - Tournament of Towns

June 10, 2024

geometryexcenterConcyclic

Problem Statement

Let

O

be the centre of the circle touching the side

AC

of triangle

ABC

and the continuations of the sides

BA

and

BC

D

is the centre of the circle passing through the points

A

B

and

O

. Prove that the points

A

B

C

and

D

lie on a circle.
(YF Akurlich)