... the orthocenter are symmetric through the bisector of the outerangle ∠A.b) In triangle ABC, the angle ∠A is equal to 60◦; O is the center of the circumscribedcircle, H is the orthocenter, ... circumscribed circle of triangle ABC, let S1be the circle symmetricto S through line BC. The orthocenter H of triangle ABC lies on circle S1(Problem 5.9)and, therefore, it suffices to verify ... P′H;hence, it passes through the midpoint of side P H.5.97. Let Ha, Hb, Hcand Hdbe the orthocenters of triangles BCD, CD A, DAB andABC, respectively. Lines la, lb, lcand ldpass...