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circumcenter, excenter and vertex collinear (Singapore Junior 2012)

Source:

July 11, 2019
geometrycollinearexcenterCircumcenter

Problem Statement

In △ABC\vartriangle ABC, the external bisectors of ∠A\angle A and ∠B\angle B meet at a point DD. Prove that the circumcentre of △ABD\vartriangle ABD and the points C,DC, D lie on the same straight line.
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