cho tam giac AOB can tai O. tren tia doi cua tia OB lay C sao cho OB=OC. tinh goc BAC
giup minh voi . khong ve can hinh dau, cac ban ve o nhap ma giai. minh can loi giai thoi
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cho tam giac abc can tai a co goc bac =50do tren tia doi cua tia bc lay diem d tren tia doi cua tia cb lay diem e sao cho bd =ba ce=ca tinh goc dae
cho tam giac abc deu ve ben ngoai tam giac cac tam giac abd vuong can tai b tam giac ace vuong can tai c tinh so goc nhon cua ade
XÉT \(\Delta ABC\)CÂN TẠI A
\(\Rightarrow\hept{\begin{cases}AB=AC\\\widehat{B}=\widehat{C}\end{cases}}\)
TA CÓ \(\widehat{A}+\widehat{B}+\widehat{C}=180^o\left(Đ/L\right)\)
THAY\(50^0+\widehat{B}+\widehat{C}=180^o\)
\(\widehat{B}+\widehat{C}=130^o\)
MÀ\(\widehat{B}=\widehat{C}\)
\(\Rightarrow\widehat{B}=\widehat{C}=\frac{130^o}{2}=65^o\)
TA CÓ \(\widehat{DBA}+\widehat{ABC}=180^o\left(KB\right)\)
\(\Rightarrow\widehat{DBA}=180^o-65^o=115^o\)
TA CÓ\(\widehat{ACE}+\widehat{ACB}=180^o\left(KB\right)\)
\(\Rightarrow\widehat{ACE}=180^o-65^0=115^o\)
XÉT \(\Delta ACE\)CÓ AC=CE (GT) =>\(\Delta ACE\)CÂN TẠI C
\(\Rightarrow\widehat{CAE}=\widehat{AEC}=\frac{180^o-115^0}{2}=32,5^0\)
XÉT \(\Delta ABD\)CÓ AB=BD (GT) =>\(\Delta ABD\)CÂN TẠI B
\(\Rightarrow\widehat{DAB}=\widehat{ADB}=\frac{180^o-115^0}{2}=32,5^0\)
TA CÓ\(\widehat{DAB}+\widehat{BAC}+\widehat{EAC}=\widehat{DAE}\)
THAY\(32,5^o+50^0+32,5^0=\widehat{DAE}\)
\(\Rightarrow\widehat{DAE}=115^0\)
Tren duong thag a lay ba diem A,O,A'(O nam giua A va A').Ve tia OB sao cho AOB=45°,tren nua mat phang co bo la duong thang a khong chua tia OB ve tia OC sao cho AOC=90°
a.Goi OB' la tia phan giac cua goc A'OC.Chung minh rang:hai goc AOB va A'OB' la hai goc doi dinh
b,Tren nua mat phang co bo la duong thang a chua tia OB ve tia OD sao cho BOD=90°.Tinh so do goc A'OB'
giup minh nha! dang can gap thank
ve hinh
cho tam giac abc can tai a tren tia doi cua tia BA lay diem D tren tia doi cua tia CA lay diem E sao cho BD=CE ve DH va EK cung vuong goc voi duong thang BC
Tren tia Ox lay hai diem A va B sao cho OA = 2cm , OB =6.5 cm. Tren tia doi cua tia Ox lay diem C sao cho OC =2.5 cm .chung to diem a la trung diem cua AB
Cac ban khong can ve hinh dau
Cho tam giac AOB tren tia doi cua tia OAlay diem C sao choOA=OC. tren tia doi cua tia OB, lay diem D sao cho OD=OB. cac tia phan giac cac goc O,C,D va O,B,A cat nhau o E . tia phan giac goc O,A, B cat BE tai F. CMR
a) tam giac AOB=tam giac COD
b)AB\\OD ; AD\\BC ; CE\\AF
c)^CEB bang nua tong 2 goc ^CAB va ^CDB
Cho 1 doan thang AB dai 4cm.Ve duong thang d la duonbg trung truc cua doan thang AB,lay O thuoc d.Qua O ve doan thang OC=2cm sao cho OC vuong goc voi d.Qua O ve doan OD=1cm sao cho OD vuong goc voi d.Chung minh C,O,D thang hang.D co phai la trung truc cua doan thang CD ko?Vi sao?(Mik can ve hinh va loi giai nhe,minh ve hinh ko chac chan,mong cac ban giup do)
bai 1: tren mot nua mat phang bo chua tia Oa ve tia Ob sao cho goc AOB=35 do va tia Oc sao cho goc AOC= 70 do
a, tia Ob co phai la tia phan giac cua goc AOC khong? vi sao?
b, ve tia OB` la tia doi cua tia OB. tinh so do goc ke bu voi goc AOB
Tren duong thang AA' lay diem O .Tren mot nua mat phang bo AA' ve tia OB sao cho goc AOB = 45o,tren nua mat phang con lai ve tia OC sao cho goc AOC = 90o.
a.Goi OB' la tia phan giac cua goc A'OC. Chung to rang hai goc AOB va A'OB' la hai tia doi dinh.
b. Tren nua mat phang bo AA' co chua OB ve OD sao cho goc BOD =90o. Tinh A'OD.
cho tam giác abc cân tại a goc a 45 do tu trung diem I cua AC ve duong thang vuong goc voi Ac cat BC o M tren tia doi AM lay N sao cho AN=BM chung minh a, goc AMC=goc BAC b, tam giac ABM= tam giac CAN c, tam giac MNC vuong can tai C