cho goc AOB. Trong AOB ve cac tia Oc ,Od sao cho AOc=BOd .chung minh BOc=AOd
b/cho ABC.goi M la mot diem thuoc canhAc ,goi E la mot diem thuoc canhAB .duong thang CE cat canh ABM. giai thich vi sao CE cat canh BMcua▲ABM
cac ban nho k va kb voi mk nhe mk se k lai cho cac bn