cm goc tao boi 2 duong phan giac cua 2 goc ngoai cua 1 tam giac bang 1 nua goc ngoai thu 3
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Cho tam giac ABC. Hai duong phan giac ngoai ( duong phan giac ngoai la duong phan giac cua goc ngoai tam giac) cat nhau tai I. CMR AI la tia phan giac goc A
Cho 1 duong thang cat 2 duong thang song song,Hay chung minh rang:
a,Cac tia phan giac cua 1 cap goc so le (hoac so le ngoai thi song song voi nhau
b,Cac tia phan giac cua 1 cap goc dong vi thi song song voi nhau.
c,Cac tia phan giac cua 1 cap goc trong cung phia(hoac ngoai cung phia) thi vuong goc voi nhau.
cho tu giac abcd biet goc a: goc b: goc c: goc d =4:3:2:1
a) tinh cac goc cua tu giac abcd
b) cac tia phan giac cua goc c va goc d cat nhau tai e. cac duong phan giac cua goc ngoai tai ca dinh c va d cat nhau tai f. tinh goc ced va goc cfd
a) Ta có: \(\frac{\widehat{A}}{4}=\frac{\widehat{B}}{3}=\frac{\widehat{C}}{2}=\frac{\widehat{D}}{1}\)
Áp dụng t/c dãy tỉ số bằng nhau ta được:
\(\frac{\widehat{A}}{4}=\frac{\widehat{B}}{3}=\frac{\widehat{C}}{2}=\frac{\widehat{D}}{1}=\frac{\widehat{A}+\widehat{B}+\widehat{C}+\widehat{D}}{4+3+2+1}=\frac{360}{10}=36\)
\(\Rightarrow\widehat{A}=144^0;\widehat{B}=108^0;\widehat{C}=72^0;\widehat{D}=36^0\)
Cho tam giac ABC co goc A khac goc B cac tia phan giac trong va ngoai cua goc C lan luot cat duong thang BA tai D va E tinh goc CED theo goc A va goc B cua tam giac ABC
cho tam giac ABC co 3 goc nhon cac duong cao AD BE CF cua tam giac ABC cat nhau tai H
a) CM: tu giac CFHD noi tiep trong 1 duong tron xac dinh vi tri tam O cua duong tron ngoai tiep tu giac CEHD
b) CM: goc FEH bang goc DEH . CM: H la tam duong tron noi tiep tam giac DEF
c) CM; CH = 4cm tinh do dai duong tron tam (o) va duong kinh hinh tron (o)
cho tam giac abc co goc a=120 do, phan giac ad. duong phan giac goc ngoai tai x cat duong thang ab tai k. goi e la giao diem cua dk va ac. tinh goc bed
cho tam giac abc co b>c.duong thang chua tian p/g cua goc ngoai dinh a cat bc o d.cm
adb=1/2(b-c)
tu b ve duong thang// ad. cm tam giac abe co 2 goc bang nhau
1.cho tam giac ABC co goc B-C=alpha phan giac AD
a) tinh gocADC,ADB theo alpha
b)Ve duong cao AH tinh goc HAD
2.chotam giac ABC,gocA =alpha,cac tia ohan giac cua B va C cat nhay tai I.Phan giac cat goc ngoai tai dinh B,C cat nhau tai K.Tia p/g goc B cat goc ngoai o dinh C.tinh cac goc BIC,BKC,BEC theo alpha.
Cho tam giac ABC .Cac duong thang chua tia phan giac cua cac goc ngoai dinh B va o dinh C cat nhau tai K.Tinh goc a biet goc BCK =50°