ve duong thang xy.Tren xy lay 2 diem I,B roi lay diem C sao cho I la trung diem cua doan thang BC. Lay diem D sao cho B la trung diem cua doan thang ID.
a) Co phai CD dai gap 3 lan IB khong?Vi sao?
b) Ve trung diem M cua IB. Vi sao diem M cung la trung diem cua CD?