Bài 35. Cho đường tròn (O), điểm A nằm bên ngoài đường tròn. Kẻ các tiếp tuyến AB, AC với đường tròn (B, C là các tiếp điểm). a) Chứng minh rằng OA vuông góc với BC. b) Vẽ đường kính CD. Chứng minh rằng BD song song với AO. c) Tính dộ dài cắc cạnh của tam giác ABC, biết OB = 2cm, OA = 4cm. 

Đun 6,0 gam CH3COOH với C2H5OH dư (xúc tác H2SO4 đặc) thu được 4,4 gam CH3COOC2H5. Tính hiệu suất của phản ứng trên.
Giải chi tiết giúp mình với ạ 
 

13. It’s a pity I can’t cook as well as my mom.

à I wish ______________________________________________________________       

11. My daughter never calls me.
à I wish _____________________________________ call me sometimes.

12. I would like my sister to improve her English speaking.

à I wish  ________________________________________________                 

13. It’s a pity I can’t cook as well as my mom.

à I wish ______________________________________________________________       

14. How long has you possessed that Chanel bag?

→ When     

15. She doesn’t join in the trip.

 -> I wish ……………………………………….……

16. I am not good at English.

 -> I wish ……………………………………….………

17. We started learning English when we were in grade 3.

→ We have     

18. It isn’t necessary to play football with my best friends today.

➔ You don’t ________________________________________.

19. “Why don’t we visit her parents next week?”

➔ You suggested ____________________________________.

20. Thanh spends 3 hours a day doing the homework.

➔ It takes …

1. I haven't been to Australia for three years.

àThe last time I ___________________________________________________________

2. It has been six months since she visited our school.

àShe hasn’t    _____________________________________________________________

3.  That house is part of the town’s heritage, but the council is demolishing it.

à I wish _______________________________________________________________

4.  He feels sorry that he can’t come to his brother’s wedding.

à He wishes ____________________________________________________________

5. Ngân doesn’t want to see Sơn.

→ Ngân avoids     

6.  It’s a pity I can’t get my visa extended.

→ I wish     

7. The last time I ate noodles was two months ago.

àI  _____________________________________________________________________

8. It haven’t  rained for four weeks

àThe last time ___________________________________________________________

9. Nam loves playing football.

àNam enjoys _________________________________________________________

10. This is my first game of tennis.

 àI haven’t     _____________________________________________________________

1. They/  have / never / watch/ that film / before

à ____________________________________________________________________ .

2. Teens/ can learn / many skills / such experiences.

à _____________________________________________________________________ .

3. They have chances/ explore/ new places / their own eyes.

à _____________________________________________________________________

4. My brother/  playing / computer games.

 à _____________________________________________________________________

5. they / sleep / when / you / phone / them?

 à _____________________________________________________________________

6. My little sister/ I / not, watching / film /  TV / 8 o’clock/  yesterday.

 à _____________________________________________________________________

7. When / we / arrive/ the fair, / the rice – cooking competition was taking place.

 à _____________________________________________________________________

8. I / drop / my mobile phone / when / I / walk / to school.

 à _____________________________________________________________________

9. What / Jamie / do / when / you / see / him?

 à _____________________________________________________________________

10. It / not rain / when / we / leave / the house / this morning.