cho tam giac ABC co gocBAC >90 do. Goi I la trung diem cua AC. Tren tia doi cua IB lay D sao cho IB=ID.
a, Chung minh tam giac AIB bang tam giac CID
b,Chung minh goc AIB nho hon goc BIC
c, Tim dieu kien cua tam giac ABC de AB vuong goc voi CD
cho tam giac abc co goc a nho hon 90 do cho tam giac abc co 2 doan thang ad vuong goc va bang ab,ae vuong goc va bang ac
a, cmr dc=be va dc vuong goc voi be
b, goi n la trung diem cua de.tren tia doi cua tia na lay m sao cho na=mn . chung minh ab=me va tam giac abc=tam giac ema
cho tam giac ABC vuong tai A , goi I la trung diem cua canh AC .tren tia doi cua tia IB lay diem D sao cho IB bang Id . chung minh
a CID bang AIB , b AD bang BC , ADsong song BC C , goi Mva N lan luot la trung diem AD va BC . chung minh M,N,I thang hang
Cho tam giac ABC vuong tai A co goc B =55 do. Goi M la trung diem cua AC. Tren tia doi cua tia MB lay diem D sao cho MD=MB
a. Tinh so do cua goc ACB
b. Chung minh tam giac AMB va tam giac DMC bang nhau
c. Chung minh CD vuong goc voi AC
1.cho tam giac ABC can tai dinh A, trung truc cua canh AC cat CB tai diem D (D nam ngoai doan BC). tren tia doi cua tia AD lay diem E sao cho AE= BD. chung minh tam giac DEC can.( goi y can chung minh CD = CE)
2. cho tam giac ABC co AB < AC, lay diem E tren canh CA sao cho CE=BA, cac duong trung truc cua cac doan thang BE va CA cat nhau tai I
a)chung minh tam giac AIB = tam giac CIE
b)chung minh AI la tia phan giac cua goc BAC
Cho tam giac ABC vuong tai A co AB=AC . Goi D la trung diem cua AC . Tren tia doi cua tia DB lay diem E sao cho DB=DE
a) Chung minh : tam giac ADB=tam giac CDE
b) Tren tia doi cua tia AB lay diem I sao cho AD = AI. chung minh : tam giac CDE = tam giac AIC
c) chung minh CI vuong goc EB
Cho tam giac ABC , AB=AC.M la trung diem cua BC .Tren tia doi tiaMA lay diem D sao cho AM=MD .
a chung minh tam giac ABM=tam giacDCM.
b chung minh AB song song BC.
c chung minh AM vuong goc BC
d tim dieu kien cua tam giac ABC de goc ADC=36do
cho tam giac abc co ab<ac,tren tia doi cua ca lay diem d sao cho cd=ab. duong trung truc cua bc,ad cat nhau tai I
a, chung minh tam giac AIB=tam giac DIC
b chung minh AI la tia phan giac cua goc BAC
c ke IE vuong goc voi AB, chung minh AE=1/2 AD
A) Vì I là đường trung trực của BC
\(\Rightarrow IB=IC\)
I THUỘC ĐƯỜNG TRUNG TRỰC CỦA AD
\(\Rightarrow AI=ID\Rightarrow\Delta IAD\)CÂN\(\Rightarrow\widehat{IAC}\)=\(I\widehat{DC}\)
XÉT TAM GIÁC ABI VÀ TAM GIÁC ICD CÓ:
AB=CD
IB=IC
IA=ID
VẬY TAM GIÁC ABI = TAM GIÁC ICD
\(\widehat{BAI=CDI}\)
\(\widehat{BAI}\)=\(\widehat{IAC}\)
AI LÀ PG BAC
C)ĐANG NGHĨ BN NHÁ
HC TỐT
cho tam giac ABC tren tia doi cua tia AB lay diem D sao cho AC= AD. tren tia doi cua tia AC lay diem E sao cho AE=AB
a) chung minh tam giac ADE= tam giac ACB
b)goi M la trung diem cua BE chung minh tam giac ABM bang tam giac AEM
c) duong thang AM cat CD tai N. Chung minh AN vuong goc CD
cho tam giac ABC co goc a nhon M la trung diem cua BC tren tia doi cua tia MA lay diem D sao cho MA=MD chung minh BAM=CDM chung minh AC=AD tren nua mat phang Bo AB ko chua C ve tia Ax vuong goc AB tren nua mat phang bo AC ko chua B ve tia Ay vuong goc AC tren tia Ax lay Diem P sao cho AP=AB tren tia Ay lay diem Q sao cho AQ=AC chung minh tam giac ABQ= tam giac APC goi giao diem cua DA va PQ la K chung minh AK vuong goc PQ