Let ABC be an acute triangle, and its altitudes AX,BY,CZ concurrent at H. Construct circles (Ka),(Kb),(Kc) circumscribing the triangles AYZ,BZX,CXY . Construct a circle (K) that is internally tangent to all the three circles (Ka),(Kb),(Kc). Prove that (K) is tangent to the circumcircle (O) of the triangle ABC.Đỗ Thanh Sơn orthocentergeometrytangent circlesconstructioncircles