MathDB

Points on semicircle

Source: Polish MO second round 2011

February 19, 2012

geometrygeometric transformationrotationgeometry unsolved

Problem Statement

Points

A,B,C,D,E,F

lie in that order on semicircle centered at

O

, we assume that

AD=BE=CF

G

is a common point of

BE

and

AD

H

is a common point of

BE

and

CD

. Prove that:

\angle AOC=2\angle GOH.