a, Xét tam giác MBD và tam giác NCE ta có : 

DM = CE (gt) 

^MBD = ^NCE (gt) 

Vậy tam giác MBD = tam giác NCE ( ch - gn ) 

=> MB = NC ( 2 cạnh tương ứng ) 

=> AM = AN 

b, Xét tam giác MAK và tam giác NAK có : 

AK _ chung 

AM = AN ( cmt ) 

Vậy tam giác MAK = tam giác NAK ( ch - cgv ) 

1+1=3 nhé khỏi cảm ơn

bạn nào giúp mk vẽ hình đc không

Xét ΔADE và ΔABC có :
AD = AB (gt)

góc DAE =góc BAC = 90 độ
AE = AC (gt)
Do đó : ΔADE = ΔABC(c − g − c)
⇒ DE = BC ( hai cạnh tương ứng )
b.
Ta có :
góc ADE =góc CDN ( hai góc đối đỉnh )
góc C= góc E
( vì ΔADE = ΔABC )
⇒ góc N = góc A 90đọ
Hay DE ⊥ BC
Vậy DE ⊥ BC

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a: Xét ΔMBD vuông tại M và ΔNCE vuông tại N có

DB=EC

\(\widehat{DBM}=\widehat{ECN}\)(ΔABC cân tại A)

Do đó: ΔMBD=ΔNCE

b: Ta có: ΔMBD=ΔNCE

=>MB=NC

Ta có: AM+MB=AB

AN+NC=AC

mà MB=NC và AB=AC

nên AM=AN

Xét ΔAMK vuông tại M và ΔANK vuông tại N có

AK chung

AM=AN

Do đó: ΔAMK=ΔANK