a) ta có : theo BĐT \(\Delta\)ta luôn có : tổng độ dài hai cạnh bất kỳ bao giờ cũng lớn hơn độ dài cạnh còn lại.

vậy áp dụng BĐT\(\Delta\)vào tam giác ABC ; ta được :

\(\hept{\begin{cases}AB+AC>BC\\AB+BC>AC\\AC+BC>AB\end{cases}}\)

b)xét \(\Delta AHB:\widehat{H}=90^o\)=>\(BA>HB\)(vì cạnh huyền là cạnh lớn nhất)

tương tự với tam giác AHC ta cũng được AC>HC vì cạnh huyền là cạnh lớn nhất

There is a unique festival of Dao ethnic group you must see – the “Dancing over fire” festival. This festival takes place every year to pray for good weather, harvests, bringing warmth to the people, dispel the cold mountainous weather. The chosen ones are strong healthy guys. The shaman will do some mysterious rituals, praying the Gods give the chosen men strength. After the shaman finish the first rituals, the men have shivers, signaling they are about to receive the strength and courage to jump and dance on the embers in front of people. The shaman drum become more and more impulsive, the men dance with stronger movements and jump on the embers. What a spectacular and unique scene, it really makes you feel closer to the gods above.
Nowadays, bullfighting (or buffalo fighting) is still one of the most famous festivals. It has been maintained and developed in the plains and some place in midland. This festival although a little bit violent but it is an indispensable features of agricultural culture in which the buffalo is an essential animal and the strength of them is one of the most crucial factors. This festival is so famous that even the guests have to come early to reserve a good seat. A clan or village owns “the champion buffalo” feel very honored, proud and have more confidence in a year filled with health, luck, good weather, harvest …

Almost all the provinces along the coastline have their own boat racing competition. According to the researchers, boat racing competitions originated from the worship to god whale, earth spirit and river spirit. It represents the love of the fishermen to the sea and the dream to conquer it. The fishermen show their strength, their solidarity and their skills in this contest.

Traditional festivals play a very important role in culture. Although many of them can not maintain the original rituals but the spirit and the meaning of them will never change in each Vietnamese mind. We inherited precious tradition from our forefathers and we will do our best to maintain and develop it in our own way.

Traveling Vietnam by motorbike to remote areas at the New Year time you’ll have more chances to join at meaningful festivals of the local hill tribes. Vietnam Motorbike Tour Expert team is ready to travel and discover the the meaning of the traditional festivals in Vietnam.

 if  you're  noi  yours it's not  someone else's

dịch:nếu bạn không phải của bạn thì không phải của người khác

chúc bạn học tốt

1. C

2.B

3.B

4.D

5.A

II/ 1, What

2.When

3.where

4. How Often

5.How Much

6. How long

7, Who 

8.What kind

9.why

10.how

lỗi sai là is đó :>

lỗi là is đó 

hok tốt

My school is ....( điền tên trường bn ) ........This Saturday, our History teachers will celebrate a History competiton. Each class votes 1 student to take part in this competition. And the law is that: The teachers will give each representative of each class a number of time, then he/she must guest the event of this time, the more you guest, the more points you get. with each event, the group will get 5 points. And the winner is the representative who get the most marks. The winner will be awarded a CD of History f Vietnam. This competition is donated by the Student's Parents society.

1. when is the festival of the sun held?

2. where is the festival celebrated?

3. how often the festival takes place?

4,5,,6,7 ko biết :D

1 Have you ever driven on the wrong side of the road?

2 My family flew back from our Hong Kong holiday two days ago.

3 Right now, the students are learning road signs in the schoolyard.

4 Jenifer usually walks to school, but this week she rides her bike.

5. The driver was so drunk that he lost control of his car.

6. If I have enough money, I would buy a racing car.

7. My father taught me to ride a bike when I was seven.

8. Transport used to be much slower three hundred years ago.

9. Saudi women weren’t allowed to drive a car until recently.

10. In South Africa, you have to let animals go first.

1. Have you ever driven
2. flew 
3. are learning 
4. walks; is riding
5. lost
6. will buy
7. taught 
8. to be 
9. to drive
10. go

1- is
2- the increased
3- earn
4- have
5- becoming
6- purchase

1. Do you enjoy maths at school?

2. I didn’t flying, but I love it now.

3. We are friends, but we don’t get on now.

4. Did John work for IBM before he came here?

5. Winters weren’t as cold as they are now.

6. She lived with her mother, but now she lives with her father.

7. I don’t do any exercise.

8. Does he play for Manchester United?