a: \(\widehat{ABC}+\widehat{ACB}=180^0-60^0=120^0\)
\(\Leftrightarrow\widehat{ICB}+\widehat{IBC}=60^0\)
hay \(\widehat{BIC}=120^0\)
b: Điểm F ở đâu vậy bạn?
Cho tam giac ABC, goc A =60 do. Tia phan giac cua goc Bva C cat cac canh doi dien tai D va E, BD va CE cat nhau tai O. Tia phan giac cua goc BOC cat BC tai F. Chung minh a, OD=OE=OF b, Tam giac DEF la tam giac deu.
cho tam giac ABC can tai C.Ke tia phan giac voi goc C cat AB tai I.Biet AC=5cm,AB=6cm. a,Chung minh tam giac ACI=tam giac BCI va AI=BI. b,Tinh do dai CI. c, Qua A va B lan luot ke cac duong thang vuong goc voiAC va BC chung cat nhau tai K.Chung minh 3 diem C,I,K thang hang
Cho tam giac ABC. Cac tia phan giac cua cac goc B va C cat nhau tai I. Chung minh rang AI la phan giac goc A
Cau 1: Cho tam giac ABC vuong tai A. Duong phan giac cua goc B cayAC tai H. Ke HE vuong goc voi BC(H thuoc BC). Duong thang EH va BCA cat nhau tai I
a) Cmr: tam giac ABH= tam giac EBH ; Cm: BH la duongtruung truc cua AE
c) So sanh HA va HC ;d) Cm: BH vuong goc voi IC . Co nhan xet gi ve tam giac IBC
Cau 2: Cho tam giac nhon ABC. Ve ra phia ngoai tam giac ABC cac tam giacdeu ABD va ACE. Goi M la giao diem cua DC va BE . Cm:
a) tam giac ABE= tam giac ADC
b) Goc BMC=120do
Cau 3: Cho tam giac ABC can tai A, goc A =100do.D la mot diem thuoc mien trong cua tam giac ABC sao cho goc DBC=10do.goc DCB=20do. Tinh goc ABD?
MK SE CM ON NHUNG BN GIUP MK BAI NAY
Cho tam giac ABC ko co goc nao >=1200 o phia ngoai tam giac ABC ve cac tam giac deu ABD va ACE
a)CM: DC=BE
b)I la giao diem cua DC va BE. Tinh so do goc BIC
cho tam giac ABC ko co goc nao >= 1200 o phia ngoai tam giac ABC ve cac tam giac deu ABD va ACE
a) CM: DC=BE
b) I la giao diem cua DC va BE. Tinh so do goc BIC
cho goc Xoy nho hon 90 do va tia phan giac Ot lay A tren Oz va M la trung diem cua OA tu M ke duong thang vuong goc voi OA cat OY o B chung minh tam giac ABO can va Ox song song voi AB
1cho hai tam giac vuong la abc va def co a=d=90 ,ac=df. hay bo sung them 1 dieu kien (ve canh hay ve goc ) de tam giac abc=tam giac def
2 cho tam giac abc can tai a (a<90) . ve bh vuong goc voi ac ( h thuoc ac) , ck vuong goc voi ab ( k thuoc ab)
a) chung minh ah=ak
b) goi i la giao diem cua bh va ck . chung minh rang ai la tia phan giac
3 tim cac cap tam giac bang nhau co tren hinh 131 sach vene 7
Bai 1 : Cho tam giac ABC vuong tai A, ke duong phan giac BM cua goc B. Duong thang di qua A va vuong goc vs BM cat BC tai P.
a, Cm BA = BP va tam giac BPM la tam giac vuong
b, So sanh AM va MC
c, Keo dai PM cat duong thang AB tai Q. Cm BM vuong goc vs QC
d, Gia su goc ACB = 30 do, BM keo dai cat QC tai K. Cm rang M cach deu 3 dinh cua tam gac APK
GIUP MINH VOI CAM ON NHIEU !^^ 
