Nine point circle

Also known as Euler's circle or Feuerbach's circle, as its name introduces itself that the nine point circle passes nine points, which are a given triangle $\triangle ABC$ 's feet of altitude dropped from three vertices $A,B$ , and $C$ , usually denoted as $H_A,H_B,H_C$ , and midpoints of three sides, as $M_A,M_B,M_C$ , and three Euler points $E_A,E_B,E_C$ .