MathDB

Concurrent lines in convex quadrilateral

Source: 239 2010 J7

July 29, 2020

geometry

Problem Statement

In a convex quadrilateral

ABCD

, We have

\angle{B} = \angle{D} = 120^{\circ}

. Points

A'

,

B'

and

C'

are symmetric to

D

relative to

BC

,

CA

and

AB

, respectively. Prove that lines

AA'

,

BB'

and

CC'

are concurrent.

Back to Problems View on AoPS