Let ABC be a triangle, d a line passing through A and parallel to BC. A point M distinct from A is chosen on d. I is the incenter of triangle ABC,K,L are the the points of symmetry of M about IB,IC. Let BK meet CL at N. Prove that AN is tangent to circumcircle of triangle ABC.Đỗ Thanh Sơn tangentcircumcircleincentergeometry