GIải:​
9/2 l = 4,5 l 
1/2 l = 0,5 l 
Sau khi đã lấy bớt và thêm vào thì tổng số xăng ở hai can là: 
13 - 2 + 4,5 = 15,5 ( l ) 
Số lít xăng can thứ nhất sau khi bớt là: 
( 15,5 + 0,5 ) : 2 = 8 ( l ) 
Số lít xăng can thứ nhất ban đầu đựng là: 
8 + 2 = 10 ( l ) 
Số lít xăng can thứ hai ban đầu đựng là: 
13 - 10 = 3 ( l ) 
Đáp số: 
Can 1: 10 lit 
Can 2 : 3 lít

Complete the second sentence in such a way that it is almost the same as the first 

1. Do we have to write all the questions?

=> Need we write all the questions?

2. Barbara is the best tennis - player in the club.

=> No one in the club plays tennis better than Barbara.

3. I haven't enjoyed myself so much for ages.

=> It's ages since I enjoy myself so much.

4. The cake was so hard that he could not eat it.

=> It was such a hard cake that he couldn't eat it.

5. Someone repaired her car yesterday. 

=> She had a car to be repaired yesterday.

6. I've never met a more intelligent man than him. 

=> He is the most intelligent man I've ever met.

7. Everyday I spend 2 hours learning English.

=> Everyday It takes me 2 hours to learn English. 

8. My grandfather bought this clock 30 years ago.

=> This clock was bought by my grandfather 30 years ago.

2. \(A=\frac{x^2-2x+2011}{x^2}=1-\frac{2}{x}+\frac{2011}{x^2}=\left(\frac{2011}{x^2}-\frac{2}{x}+\frac{1}{2011}\right)+\frac{2000}{2011}=\left(\frac{\sqrt{2011}}{x}-\frac{1}{\sqrt{2011}}\right)^2+\frac{2000}{2011}\)

\(\Leftrightarrow A\ge\frac{2000}{2011}\Rightarrow MinA=\frac{2000}{2011}\Leftrightarrow\frac{\sqrt{2011}}{x}=\frac{1}{\sqrt{2011}}\Leftrightarrow x=2011\)

a) Xét tam giác ABD và tam giác EBD có

          góc BAD=BED=90 độ

         BD cạnh chung

         góc ABD=EBD(gt)

Vậy tam giác ABD=EBD(cạnh huyền-góc nhọn).

b) Vì tam giác ABD=EBD nên

AD=ED(cạnh tuognư ứng) => D là điểm thuộc đuognừ trung trực của AE (1)

AB=EB9cạnh tương ứng) => B là điểm thuộc đường trung trực của AE (2)

Từ (1) và (2) suy ra BD là đường trung trực của AE

Điền dạng đúng của từ cho trong ngoặc.

My mother heats a pan and stir-fried the beef. ( HOT )

Make question for the underlined words

1 . Her date of birth is on October 20 th

-> When is her birthday?

2. My father is a journalist

-> What does your father do?

3. His telephone number is 3 567 654

-> What is his telephone number?

4. She will be 14 on her next birthday

-> When will she be 14?

or How old will be she on her next birthday?

Vì ko bít gạch chân ở đâu nên mik làm đại có gì sai thì cứ ns nhé.

Reorder the words to make meaningful sentences

4.her/ can / beautiful / a / garden / from / see / you / room

=> You can see a beautiful garden from her room.

5. colder / is / winter / summer / than

=> Winter is colder than summer.

6. tallest / my / is / the / family / in / brother / person / my

=> My brother is the tallest person in my family.

7. lives / very / from / he / far / office / his

=> He lives very far from his ofice.

8. will / party / see / friends / old / they / at / the / their / ?

=> Will they see their old friends at the party?

9. afternoon / often / play / badmiton / they / the /  in  / . /

=> They often play badminton in the afterrnoon.

10. raise / grow / the / vegetables / cattle / and / farmers 

=> Farmers grow vegetables and raise the cattle.

Exercise 16 : Make question

1. Hoa ' s father is a farmer.

=> What does Hoa's father do?

2. The doctor is working in the hospital.

=> Where is the doctor working?

3.The dentist takes care of people ' s teeth.

= > Who takes care of people' s teeth?

4. They are playing games with their friends.

= > Whom are they playing games with?

5. She will come here at 10 o ' clock.

=> What time will she come here?

6/ He is sad beacause he gets bad English marks.

=> Why is he sad?

7. They travel around the wolrd by plane. 

=> How do they travel around the world?

8. She is thirteen years old. 

=> How old is she?

9. It is about three kilometers from my house to my school. 

=> How far is it from your house to your school?

10.They are going to stay in Hue for a week. 

=> How long are they going to stay in Hue?

Bài 1 : Tính giá trị của các biểu thức sau đã bỏ dấu ngoặc :

A= (3,1 - 2,5) - (- 2,5 + 3,1) = 3,1 - 2,5 + 2,5 - 3,1 = 0

B= (5,3 - 2,8) - (4 + 5,3) = 5,3 - 2,8 - 4 - 5,3 = - 6,8

C= - (251.3 + 281) + 3.251 - (1 - 281) = - 753 - 281 + 753 + 280 = - 1

D= - (35 + 34) − ( − 34 + 25) = - 35 - 34 + 34 - 25 = - 60

vớ vẩn cái j 

toán dân gian việt nam đó 

32! = 1.2.3.4...10....32 = (..0)

Vậy 32! có chữ số tận cùng là 0.

Viết các phương trình phân tử và ion rút gọn (nếu có) xảy ra trong dung dịch giữa các chất sau :

a) Na₂CO₃ + Ca(NO₃)₂ -> CaCO₃ + 2NaNO₃

b) FeSO₄ + 2NaOH -> Na₂SO₄ + Fe(OH)₂   

c) NaHCO₃ + HCl -> H₂O + NaCl + CO₂   

d) NaHCO₃ + NaOH -> H₂O + Na₂CO₃ 

e) K₂CO₃ + NaCl -> ko có PTHH   

g) Pb(OH)₂ + 2HNO₃ -> 2H₂O + Pb(NO₃)₂ 

h) Pb(OH)₂ + 2NaOH -> Na₂\(\left[Pb\left(Oh\right)_4\right]\)

i) CuSO₄ + Na₂S -> CuS + Na₂SO₄.