cho goc mOn = 86 .Tren tia Om lay diem A,qua A ve tia At sao cho goc mAt = 86 (Tia At nam trong goc mON)
a)Tia At co // voi tia On khong ? Vi sao?
b)Ve Ah vuong goc voi On (h thuoc On).Chung minh Ah vuong goc At
c) goc OAh = ?
d) Goi I la trung diem cua Ah .Duong trung truc d cua doan Ah cat OA tai b .Chung minh goc OBI = goc OAt