2B = 2 + 2^2 + 2^3 + 2^4 + ... + 2^2009 /1 - 2^2009

=> 2B - B = B = 1 - 2^2009 / 1 - 2^2009 

=> B = 1

~~~Đoàn Ngọc Minh Hiếu~~~

1.search

2.music 

3.doing

Cậu xem tổng có 3 thừa số và thừa số lớn nhất là 1/148.

Cậu thấy giả sử tăng mấy thừa số kia bằng thừa số đó thì chúng cũng chỉ bằng 3/148<1/3

Thế nên  1/150+1/149+1/148 nhỏ hơn 1/3

Có bài đọc hiểu ko bạn?

Cho mình xin các động từ ở part I 

  Mai has just got her new timetable. Her lessons begin at 7 each morning and last until eleven twenty. After the first three lessons she has absence for twenty minutes. During this time, Mai usually talks to her friends. She has five periods  in the morning but she is free in the afternoon. Her favorite subjects are English and Math. The first term last about four months, from September to December. 

Điền dạng đúng của từ trong ngoặc:

1. Pupils are very interested in outside class.....activities..................(act)

2. They take an....active....part in them. (act)

3. My brother wants to become a.......historian...................(history)

Tìm lỗi sai và sửa lại:

1. Sing is my favorite pastime. I'm a member of the school band.

Sing => Singing

2. Ba is the president of the stamp collector club.

collector => collectors'

3. If they have any new stamps, they bring it to school.

bring => will bring 

4. Some students are eating and drinking as well as chat.

chat => chatting

5. After work I usually feel tired so I want relax.

relax => to relax

6. Thanks for the telephone number, I'll call you sometimes.

sometimes => some time

7. My bedroom is more bigger than my sister's.

more bigger => bigger

8. My uncle grows vegetables and raises cattles on his farm.

cattles => cattle

California is the __most____(1) famous state in the USA. It isn't ___the__(2) biggest state; that's Alaska. But it __has____(3) the largest population and it's certainly the most important state ___in___(4) the US economy. It's richer __than____(5) most countries in the world. The coast has __one____(6) of the best climates in the USA; ___it___(7) is warmer and dryer than most places. Some people would also __say____(8) it's the most beautiful ! But California has some __criminals____(9); Los Angeles has one of the worst crime rates ____of___(10) any US city.

Nếu ngày 12 là thứ 2 thì ngày 19 cũng là thứ 2

Poli (vinyl axetat) (PVA) được dùng để chế tạo sơn, keo dán. Monome dùng để trùng hợp PVA là

A. CH₃COOCH=CH₂

B. CH₂=CHCOOCH₃

C. HCOOCH=CH₂

D. CH₃COOCH₃