c)
\(BM=\frac{1}{2}\)
Vì BM là trung tuyến \(=\frac{1}{2}\)cạnh huyền AC

xét tam giác ABM và tam giac AMD có

AB = AD ( gt)

AM chung

BM = MD ( M là trung điểm BD )

suy ra 2 tam giác bằng nhau

a) xét tam giác ABC và tam giác DMC có:

CA=CD

góc ACB= góc DCM ( đối đỉnh)

BC=CM

=> tam giác ABC=tam giác DMC (c.g.c)

b) theo a) tam giác ABC=tam giác DMC=> góc A= góc D

mà đây là 2 góc so le trong nên MD//AB

c) Xét tam giác ICB và tam giác NCM có:

góc B= góc M ( tam giác ABC= tam giác DMC)

BC=MC

góc ICB= góc NCM ( đối đỉnh)

=> tam giác ICB= tam giác NCM(  g.c.g)

=> IB=MN

Mà AB=MD ( tam giác ABC= tam giác DMC)

=> AB-IB= MD-MN

=> AI=ND

Cảm ơn bạn Hằng Lê Nguyệt

mình hướng dẫn nhé 

a) ta chứng minh \(\Delta NPC=\Delta NMA\)

có \(NP=MN\);  \(AN=NC\); \(\widehat{ANM}=\widehat{CNP}\) ( 2 góc đối đỉnh)

\(\Rightarrow AM=PC\)( 2 cạnh tương ứng)

mà \(AM=MB\)  \(\Rightarrow PC=MB\) (Đpcm)

b) ta có: \(\Delta NMA=\Delta NPC\)

\(\Rightarrow\widehat{NCP}=\widehat{NAM}\) ( 2 góc tương ứng)

\(\Rightarrow AM\) song song \(PC\)  ( 2 góc ở vị trí so le trong)

hay \(AB\) sogn song \(PC\)

c) ta có \(MN\) là đường trung bình của \(\Delta ABC\)

\(\Rightarrow BC=2MN\) và \(BC\)song song  \(BC\)

mafia làm đúng rồi mình chỉ bổ sung hình vẽ thôi là bài hoàn thiện 

Mình ko biết nói hoạt giải trí hay gì nên mình ghi đại bài này nha

In my freetime, I love to dance. When I was a little girl I danced all the time. My mother put me in dance school  when I was 3 years old. My first dance dress was pink and it was love a ballet dress. Our dance group’s firts show was when we were 5 years old. We looked pinguis. In 9 years we have had a lot of dance shows. I have danced for 9 years in the same dance company. But now everyone has joined other dance groups.

When I dance I forget everything else and I focus only on danceing. It was relaxing and it makes me happy. I to take care of my body and dancing enhances your condition.

But now when I’m in High school  I do not have time to dance. It’s so sad. I miss dancing . I hope that I have time to dance again day

Tham khảo :

After school is a very good time for all the students to rest! Uhm... When I get away from the school, I will meet my friends to play football. I always do that except for Sunday. I to run with the ball, I to kick and I to talk and laugh with my friends. Then, I will go home to help my mom with the housework. I'm a bit bored and tired of it, but I still have to do. Haizzz... Next, I will eat a very very very delicious dinner. Of course, it's made from my mom. After having a very very very delicious dinner, I will do my homework. I often spend two hours doing it. And at the end of the day, I will go to bed, to rest, to sleep, to dream.