A = 2/5 + 2/10 + 2/20 + ... 2/320 

=> 2A= (2/5 + 2/10 + 2/20 + ... 2/320 ) x 2 

           = 4/5+ 2/5 + 2/10 + ... + 2/160 

=> 2A - A= 4/5 - 2/320 

=> A= 128/160  - 1/160 = 127/160

Số nghịch đảo của -6/11 là : -11/6

Một vòng văn bản riêng biệt chưa chắc đã đúng hay sai vì nó cần phải được đặt trong ngữ cảnh rộng hơn để kiểm tra tính chính xác và logic. Để xác định tính đúng sai, ta cần xem xét ngữ cảnh, căn cứ, và dẫn chứng liên quan đến nội dung của vòng văn bản.

a,

- Tính AH:

Áp dụng hệ thức liên quan tới đường cao vào Δvuông ABC, ta được:

AH²= BH.CH = 9.16 = 144

⇒ AH=12 (cm)

- Tính AB:

Áp dụng định lý pytago vào tgv AHB, ta được :

AB² = AH² + BH² =9²+12²= √225 =15 (cm)

- Tính AC:

Áp dụng định lý pytago vào Δ vuông AHC, ta được:

AC²=AH² + CH² = 16² + 12² = √400 =20 (cm)

Take

My friend tom wished he spoke English well

he is not a film star-> he wishes he had been a film star

The new central heating is being installed by the men on Saturday.

1. fashionable
2. designers

1. Peter was playing a video game when his brother entered the room.
2. I was studying for my English test when my mother came home from work.
3. Emma was washing the dishes when the telephone rang.
4. I ate a sandwich while my parents were drinking coffee.
5. I was watching a DVD when my cat jumped on me.
6. Yesterday at 9.30 p.m, my parents were sitting in the garden and drinking some Coke.
7. The chambermaid was making my bed in the hotel and cleaning the bathroom.
8. Someone knocked on the door while I was reading the newspaper.
9. My brother was buying a lot of books when he lived in Cambridge.
10. William did not meet Sally at the airport last Sunday.
11. Jerry was having dinner when the lights went out.
12. The girl felt ill so she didn't go to work.
13. I was eight years old when my elder sister taught me how to ride a bike.
14. John did not go to school last week because he was ill.
15. I didn't know anything about the plane crash in my neighborhood because I was working inside at that time.
16. Susan was studying in her room when she heard the noise.
17. What were they doing at eleven p.m. last night - it was so noisy?
18. A: How did Anne break her leg?
B: She was riding her horse when she fell and landed on her leg.
A: Did she go to the hospital?
19. A: When did you see Peter?
B: While I was doing my shopping at the supermarket.
20. A: I called you last night but you didn't answer. Where were you?
B: I was jogging in the park.

C. similar