IMO Shortlist 2011 problem G6
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Avg: 8,0 Let
be a triangle with
and let
be the midpoint of
. The angle bisector of
intersects the circle through
and
at the point
inside the triangle
. The line
intersects the circle through
and
in two points
and
. The lines
and
meet at a point
, and the lines
and
meet at a point
. Show that
is the incentre of triangle
.
Proposed by Jan Vonk, Belgium and Hojoo Lee, South Korea
be a triangle with
and let
be the midpoint of
. The angle bisector of
intersects the circle through
and
at the point
inside the triangle
. The line
intersects the circle through
and
in two points
and
. The lines
and
meet at a point
, and the lines
and
meet at a point
. Show that
is the incentre of triangle
.Proposed by Jan Vonk, Belgium and Hojoo Lee, South Korea
Izvor: Međunarodna matematička olimpijada, shortlist 2011
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