Math: Geometry Problem 1005:
Triangle, Circle, Circumcenter, Interior and Exterior
Angle Bisector, 90 Degree, Perpendicular. Level: School, College.
The figure below shows a triangle ABC
with circumcenter O. BD and BE are the interior and exterior
bisectors of angle B. If Q is the circumcenter of triangle DBE,
prove that the measure of angle OBQ is 90 degrees.