Go Geometry Problems: Circumcenter

Online Geometry Problem 706: Triangle, Cevian, Three Circumcenters, Circumcircles, Concyclic Points. Level: High School, Honors Geometry, College, Mathematics Education

In a triangle ABC, O is the circumcenter, and D is a point on AC. If E and F are the circumcenters of triangles ABD and BDC, respectively, prove that the points B, E, O, and F are concyclic. (See the figure below.) 

Triangle, Circumcenters, Concyclic points
 

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