Cho tam giac ABC.Tu trung diem D cua canh BC.Ke duong vuong oc voi phan giac cua goc A cat AB tai M,AC tai N
a) Chung minh;BM=CN
b) Biet AB=C,AC=BTinh AM,BM(gia su B>C) theo a va b
CAC BAN GIUP MINH NHA MAI MINH PHAI NOP ROI AI LAM GIUP MINH THI MIH LIKE CHO
