Let ABC be a triangle with E being the centre of its Euler circle. Through E, construct the lines PS,MQ,NR parallel to BC,CA,AB (R,Q are on the line BC,N,P on the line AC,M,S on the line AB). Prove that the four Euler lines of triangles ABC,AMN,BSR,CPQ are concurrent.Nguyễn Văn Linh geometryEuler LineconcurrentEuler Circle