Question

cho tam giac ABC co AB>AC, ke trung tuyen AM. Doan thang vuong goc voi tia p/g goc A cat AB,AC lan luot O E,F. Ke AH vuong goc EF.CMR

a)HE=HF

b)2gocBME=goc ACB- goc B

c)EF^2/4+AH^2=AE^2

d)BE=CF