Câu 1:
TXĐ:D=R

\(f\left(-x\right)=2\cdot\left(-x\right)^4-3\cdot\left(-x\right)^2+1\)

\(=2x^4-3x^2+1=f\left(x\right)\)

=>f(x) là hàm số chẵn

1) Vì x=25 thỏa mãn ĐKXĐ nên Thay x=25 vào biểu thức \(A=\dfrac{\sqrt{x}-2}{x+1}\), ta được:

\(A=\dfrac{\sqrt{25}-2}{25+1}=\dfrac{5-2}{25+1}=\dfrac{3}{26}\)

Vậy: Khi x=25 thì \(A=\dfrac{3}{26}\)

2) Ta có: \(B=\dfrac{\sqrt{x}-3}{\sqrt{x}+1}+\dfrac{2x+8\sqrt{x}-6}{x-\sqrt{x}-2}\)

\(=\dfrac{\left(\sqrt{x}-3\right)\left(\sqrt{x}-2\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)}+\dfrac{2x+8\sqrt{x}-6}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)}\)

\(=\dfrac{x-5\sqrt{x}+6+2x+8\sqrt{x}-6}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)}\)

\(=\dfrac{3x+3\sqrt{x}}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)}\)

\(=\dfrac{3\sqrt{x}\left(\sqrt{x}+1\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)}\)

\(=\dfrac{3\sqrt{x}}{\sqrt{x}-2}\)

câu 3 chứ

1 C

2 C

3 C

4 A

5 C

6 B

7 C

8 B

9 C

10 A

11 B

12 A

13 C

14 B

15 A

16 C

17 B

18 A

19 B

20 B

II

1 A

2 C

3 B

4 C

5 B

III

1 second

2 better

3 longest

4 beautiful

5 nationality

a: \(=\dfrac{x^2+x-2x+2-2}{\left(x-1\right)\left(x+1\right)}=\dfrac{x^2-x}{\left(x-1\right)\left(x+1\right)}=\dfrac{x}{x+1}\)

1 ) the city is hit at two in the morning by the earthquake 
2 ) the plane had taken off before they arrived at the airport 
3) because there was a loud noise next to my door last night , I couldn't sleep 
4)If We protect environmemt , We will have a better place to live
5 ) because factories dump waste into rivers and lake , Many rivers and lakes are poisoned
6) English is spoken all over the world 

A₁ = 2T₁ = 4G₁ = 8X₁

=> (A₁ + T₁) / (G₁ + X₁) 

= (A₁ + A₁/2) / (A₁/4 + A₁/8)

= 4

-> A/G = 4

a) \(x^2+2x+3=\left(x^2+2x+1\right)+2=\left(x+1\right)^2+2\ge2\)

Dấu "=" xảy ra khi \(\left(x+1\right)^2+2=2\Rightarrow x=-1\)

Vậy \(MinA=2\)khi \(x=-1\)

c) \(4x^2-4x+5=\left(4x^2-4x+1\right)+4=\left(2x-1\right)^2+4\ge4\)

Dấu "=" xảy ra khi \(\left(2x-1\right)^2+4=4\Rightarrow x=\dfrac{1}{2}\)

Vậy \(MinC=4\) khi \(x=\dfrac{1}{2}\)

2. You didn't remember turning off the TV last night, did you?

3. The countryside suffers much less pollution than the city.

4. Why don't you go to work by bike?

6. More trees will be planted along this street.

7. Overpopulation causes a lot of social problems in this area, doesn't it?

8. Pollution is the most serious problem, isn't it?

9. Did a group of foreigners visit slums last week?

 câu 1, 5, 10 thấy đã làm rồi nên mình không có làm lại nha. 

2. You didn't remember turning off the TV last night, did you?

3. The countryside suffers much less pollution than the city.

4. Why don't you go to work by bike?

6. More trees will be planted along this street.

7. Overpopulation causes a lot of social problems in this area, doesn't it?

8. Pollution is the most serious problem, isn't it?

9. Did a group of foreigners visit slums last week?