cho tam giac ABC nhon co 3 duong cao AD , BE , CF cat nhau tai H CMR a)DB*DC=DH*DA.b)tam giac ABC dong dang voi tam giac AEF.c)DH/AD +HE/BE+HF/CF=1.d)  H la giao diem cac duong phan giac cua tam giac DEF

cho tam giac ABC tren cac canh BC,CA,AB lay cac diem D,E,F sao cho AD,BE,CF cat nhau tai H. CMR: AH/AD+BH/BE+CH/CF=2

cho tam giac ABC deu. Tren tia doi cua tia AB lay diem D va tren tia doi cua tia AC lay diem E sao cho AD=AE. Goi M, N, H, Q theo thu tu la trung diem cua cac doan thang BE, AD, AC, AB.

CM: a) Tu giac BCDE la hinh thang can.

b) Tu giac CNEQ la hinh thang

c) Tren tia doi cua tia MN lay diem N' sao cho MN'=MN. Cm BN' vuong goc voi BD, EB=2MN.

d) Tam giac MNH la tam giac deu

cho tam giac ABC tren canh BC,CA,AB lay cac diem D,E,F sao cho AD,BE,CF cat nhau tai H.  CMR AH/AD+BH/BE+CH/CF

Cho tam giac deu ABC. Tren canh AB lay diem D sao cho AD=1/3 AB. Tu D ke duong thang vuong goc AB cat A o E, qua E ke duong thang vuong goc AC cat BC o F. Chung minh. a, DF vuong goc BC. b, Tam giac DEF la tam giac deu

Cho tam giac deu ABC. Tren canh AB lay diem D sao cho AD=1/3 AB. Tu D ke duong thang vuong goc AB cat A o E, qua E ke duong thang vuong goc AC cat BC o F. Chung minh. a, DF vuong goc BC. b, Tam giac DEF la tam giac deu

Cho tam giac deu ABC. Tren canh AB lay diem D sao cho AD=1/3 AB. Tu D ke duong thang vuong goc AB cat A o E, qua E ke duong thang vuong goc AC cat BC o F. Chung minh. a, DF vuong goc BC. b, Tam giac DEF la tam giac deu

Cho tam giac ABC,AB>AC,tren canh AB lay diem E sao cho BE=AC.Goi I,D,F theo thu tu la trung diem CE,AE,BD.CMR tam giac IDE can , goc BAC=2IDE

Cho tam giac ABC,AB>AC,tren canh AB lay diem E sao cho BE=AC.Goi I,D,F theo thu tu la trung diem CE,AE,BD.CMR tam giac IDE can , goc BAC=2IDF