MathDB

Again a geometry in RMO

Source: RMO 2018 P1

October 28, 2018

geometrycircumcircleangle bisector

Problem Statement

Let

ABC

be an acute angled triangle and let

D

be an interior point of the segment

BC

. Let the circumcircle of

ACD

intersect

AB

at

E

(

E

between

A

and

B

) and let circumcircle of

ABD

intersect

AC

at

F

(

F

between

A

and

C

). Let

O

be the circumcenter of

AEF

. Prove that

OD

bisects

\angle EDF

.

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