임의의ㅁABCD에중점을연결한ㅁ을P,Q,R,S라고하면△AQP∽△ABD(AA닮음)따라서∠AQP=∠ABD그런데동위각의위치이므로QP//BD..①,마찬가지로QR//PS..② ①,②에의해
당신은 어느 그룹입니까?