Let be an acute triangle with
. Let
be its cirumcircle,
its orthocenter, and
the foot of the altitude from
. Let
be the midpoint of
. Let
be the point on
such that
and let
be the point on
such that
. Assume that the points
,
,
,
and
are all different and lie on
in this order.
Prove that the circumcircles of triangles and
are tangent to each other.
(Ukraine)