Ve hai tia doi nhau Ox va Oy.Lay cac diem A thuoc tia Ox,diem B thuoc tia Oy;diem C sao cho diem B nam giua hai diem O va C.
a,Ke ten cac cap tia doi nhau(cac tia trung nhau chi ke ten mot lan).
b,Ke ten cac tia trung voi tia Ay.
c,Lay diem D sao cho ba diem B,O,D khong thang hang.Noi D voi A.Ke ten cac doan thang co trong hinh ve?