1 it's necessary for me to clean his table

-> do I need to clean his table?

2 she has just written an article about the accident

-> an article about the accident hasjust been written by she

3 we haven't eaten seafood since last summer vaction

-> we last ate seafood last summer vacation (?)

4 they haven't learned english for 2 years

-> it's  2 years since they didnt learn English

5 she left without leaving any message

-> she left as she didnt leave any message (?)

6 although his leg was broken , he managed to come on time

->in spite of the broken leg,he managed to come on time

1. She hasn’t written to me for a long time 

à It’s a long time since she wrote to me

2. It's 3 months since he wrote to me. 

à He hasn’t written to me for 3 months

3. The last time I was aboard was in the summer of 1978. 

à I haven’t been aboard since in the summer of 1978

4. I haven't seen him for 2 months. 

 à I last saw him 2 months ago

5. I haven't been to a concert for over a year.  

The last time i was at a concert was over a year ago

6. It’s over six months since John had his hair cut. 

John hasnt had his hair cut for over six months

7. I haven’t enjoyed myself so much for years 

à It is a year since i enjoyed myself so much

1. Thousands of people have to build that castle for him for years.

=>That castle has to be built for him thousands of people for years

2. She has never read this book before.

=>It is the first time she has read this book

3. He failed in the examination last year.

=>He did not pass in the examination last year

4. I haven't eaten this kind of food before.

=>This is the first time I has eaten this kind of food

5. His parents made him study for his exam.

=>He was made to study by his parents

6. I don't really want to go to the museum.

=>I'd rather not  go to the museum

7. The fire has destroyed many houses.

=>Many houses have been destroyed by the fire

8. May I borrow your pen?

=>Would you mind if I borrowed your pen?

9. I started work for the company a year ago.

=>I've worked for the company a year ago

10. She didn't say a word as she left the room.

=>She left the room without saying a word

a.XétΔABD và Δ ABE
BAE chung
ABD= AEB(cùng chắn cung BD)
=> ΔABD ~ Δ AEB(g-g)
\(\dfrac{AB}{AD}\)=\(\dfrac{AE}{AB}\)
=> AB.AB=AD.AE
=> AB²= AD.AE 
OBA=90⁰(AB là tiếp tuyến)
OCA=90⁰(AC là tiếp tuyến)
=>OA là đường trung trực của BC
=>OA vuông góc BC tại H
b. Ta có Δ OBA vuông tại B,đường cao BH
AB²=AH.AO (hệ thức lượng)
mà AB²=AD.AE(cmt)
=>AD.AE=AH.AO
Xét Δ ADH và Δ AEO
EAO chung
\(\dfrac{AD}{AO}\)=\(\dfrac{AH}{AE}\)(cmt)
=>Δ ADH ~ Δ AEO (c-g-c)
=>\(\widehat{AEO}\)=\(\widehat{AHD}\)
=>tứ giác OHDE nội tiếp( góc ngoài tứ giác nt= góc trong đối đỉnh)

Đốt cháy hoàn toàn 15,6 g hỗn hợp 2 kim loại Al và Mg cần vừa đủ 8,96 lit O2(đktc).Tính % khối lượng mỗi kim loại trong hỗn hợp đầu

 Tính khối lượng của các oxit sinh ra sau phản ứng