IMO Shortlist 2011 problem G5
Avg:
Avg:
Let
be a triangle with incentre
and circumcircle
. Let
and
be the second intersection points of
with
and
, respectively. The chord
meets
at a point
, and
at a point
. Let
be the intersection point of the line through
parallel to
and the line through
parallel to
. Suppose that the tangents to
at
and
meet at a point
. Prove that the three lines
and
are either parallel or concurrent.
Proposed by Irena Majcen and Kris Stopar, Slovenia
























Proposed by Irena Majcen and Kris Stopar, Slovenia
Izvor: Međunarodna matematička olimpijada, shortlist 2011