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Brazil geometry
Problem
Let be an acute triangle and is orthocenter. Let be the intersection of and and be the intersection of and . The circumcircle of meets the circumcircle of at . Prove that the angle bisectors of and concur at a point on line .

Solution
By the angle bisector theorem, it suffices to prove that . We have and , so triangles and are similar. Thus
Techniques
Triangle centers: centroid, incenter, circumcenter, orthocenter, Euler line, nine-point circleTriangle trigonometryCyclic quadrilateralsCirclesConcurrency and CollinearityAngle chasing