Y by Adventure10, Mango247
Let
be a triangle with circumcircle
and let l be a line which does not intersect
. Let
be the foot of the perpendicular from the centre of
to l. The side-lines
and
intersect l, respectively, at the points
and
different from
. Prove that the circumcircles of triangles
and
have a common point different from
or are mutually tangent at
.













