cho duong tron tam O duong kinh AB .Ve hai day AM va BN song song voi nhau sao cho so do BM nho hon 90 do .Ve day MD song song voi AB.Day DN cat AB tai E. Tu E ve 1 duong thang song song voi AM cat duong thang DM tai C. Chung minh
a)AB vuong goc DN
b)BC la tiep tuyen cua duong tron (O)