Intersecting Circles and a Right Angle

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Let A, B, C, and D be points on a circle with center O. Let the lines AB and CD meet at M. Let the circumcircles of AOC and DOB meet at K apart from O. Then is .


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Contributed by: Jay Warendorff (March 2011)
Open content licensed under CC BY-NC-SA



See a problem from Russia 1995.

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