Cho tam giac, vuong tai A co AB<BC.Tren canh BC lay diem E sao cho BE=BA.
a) Chung minh tam giac BAF= tam giac BEF. Tu do suy ra EF vuong goc BC.
b)AE cat BF tai H.Chung minh H la trung diem ae.
c) Ve tia Bx la tia doi cua tia BC,Bt la tia phan giac cua goc ABx.
Chung minh Bt song song AE.