Go Geometry Problem Problem 464: Square, Center, Arc, Angle, 120 Degrees

The figure shows a square ABCD with center O. It contains arcs AEFC, BFD, and BED drawn with centers at D, A and C, respectively. Lines CE and FD meet at G. Prove that the measure of angle DOG is 120 degrees.
 

Square, Center, Arc, 120 degrees
 

Dynamic Geometry of Problem 464

Interactive construction created with GeoGebra by Tim Brzezinski

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