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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 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
cho tam giac ABC nhon, cac duong cao AD,BE,CF cat nhau tai H.Tren cac doan HB,HC lay cac diem M,N tuy y sao cho:HM=CN.CMR:duong trung truc cua MN luon di qua 1 diem co dinh
cho tam giac ABC.Tren canh AB,AC lay cac diem D,E sao cho BD=CE.Goi M,N,I,K theo thu tu la trung diem cuaDE,BC,BE,CD
a,Tu giac MINK la hinh gi? vi sao
b,Doi G,H la giao diem cua IKvoi AB va AC.CM tam giac AGH can
Cho tam giac ABC.D thuoc AB sao cho DA= 1/3 AB. F thuoc AC. FC=1/3AC. E thuoc BC sao cho BE=1/3BC. AE;AD;BF cat nhau tao thanh 1tam giac. CMR S tam giac do=1/7 S ABC