In an acute-angled triangle ABC,D is the foot of the altitude from A. Let D1 and D2 be the symmetric points of D wrt AB and AC, respectively. Let E1 be the intersection of BC and the line through D1 parallel to AB . Let E2 be the intersection ofBC and the line through D2 parallel to AC. Prove that D1,D2,E1 and E2 on one circle whose center lies on the circumscribed circle of △ABC. geometryConcycliccyclic quadrilateral