MathDB
Convex pentagon

Source: MEMO 2017 I3

August 25, 2017
geometry

Problem Statement

Let ABCDEABCDE be a convex pentagon. Let PP be the intersection of the lines CECE and BDBD. Assume that PAD=ACB\angle PAD = \angle ACB and CAP=EDA\angle CAP = \angle EDA. Prove that the circumcentres of the triangles ABCABC and ADEADE are collinear with PP.