MathDB

lines concurrent in tetrahedron

Source: Bulgaria 1979 P2

June 17, 2021

geometry3D geometrytetrahedron

Problem Statement

Points

P,Q,R,S

are taken on respective edges

AC

,

AB

,

BD

, and

CD

of a tetrahedron

ABCD

so that

PR

and

QS

intersect at point

N

and

PS

and

QR

intersect at point

M

. The line

MN

meets the plane

ABC

at point

L

. Prove that the lines

AL

,

BP

, and

CQ

are concurrent.

Back to Problems View on AoPS