cho tam giac ABC co AB nho hon AC D la trung diem BC tren tia doi DA lay E sao cho DA=DE

chung minh rang 

a) tam giac ABC= tam giac ECD 

b)EC lon hon AC 

c) goc DAB nho hon goc DAC

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 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 AB be hon AC, AD laf tia phan giac cua goc BAC(D thuoc BC). Tren canh AC lay diem E sao cho AE=AB.C/m rang tam giac ABD=tam giac AED, CD lon hon DB

Cho tam giac ABC co goc A lon hon 90 do. Ke DA vuong goc voi AB va DA=AB ( tia AD nam giua 2 tia AB,AC).Ke AE vuong goc voi AC va AE=AC ( tia AE nam giua 2 tia AB,AC). Ke AH vuong goc voi BC va keo dai cat De tai M. CM MD=ME

cho tam giac ABC co goc BAC lon hon hoac bang 60 do

  C/m : AB+AC < 2BC

cho tam gia abc co m la mot diem bat ki trong tam giac. chung minh: MA+MB+MC

a) lon hon nua chu vi tam giac abc

b) nho hon chu vi tam giac abc

cho tam giac abc co goc a be hon 90 do. tren nua mat phang bo ab khong chua diem ac ve tam giac abd vuong can tai a. goi i la giao diem cua cd va be, m la giao diem cua cd va ab n la giao diem cua ac va be chung minh rang ia la tia phan giac goc min