Let be a triangle with circumcircle
and incentre
. Let the line passing through
and perpendicular to
intersect the segment
and the arc
(not containing
) of
at points
and
, respectively. Let the line passing through
and parallel to
intersect
at
, and let the line passing through
and parallel to
intersect
at
. Let
and
be the midpoints of
and
, respectively. Prove that if the points
,
, and
are collinear, then the points
,
, and
are also collinear.
(U.S.A.)