MathDB

lines concurrent with external bisector

Source: Iberoamerican Olympiad 2008, problem 2

September 24, 2008

trigonometryprojective geometrygeometrytrig identitiesLaw of Sinesangle bisectorgeometry proposed

Problem Statement

Given a triangle

ABC

, let

r

be the external bisector of

\angle ABC

P

and

Q

are the feet of the perpendiculars from

A

and

C

r

. If CP \cap BA \equal{} M and AQ \cap BC\equal{}N, show that

MN

r

and

AC

concur.