1. D

2. D

3. A

4. A

5. D

1. C

2. B

3. C

4. C

5. C

6. A

7. C

8. B

9. D

10. B

11. D

12. had climbed

1.C

2.C

3.A

4.D

5.C

\(\sqrt{9x^2-6x+1}=x+4\)

ĐK: \(x\ge-4\)

\(\Leftrightarrow\sqrt{\left(3x-1\right)^2}=x+4\)

\(\Leftrightarrow\left|3x-1\right|=x+4\)

\(\Leftrightarrow\left[{}\begin{matrix}3x+1=x+4\\3x+1=-x-4\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}2x=3\\4x=-5\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}\\x=-\dfrac{5}{4}\end{matrix}\right.\)

Áp dụng định lý Pytago vào tam giác vuông ABC:

\(BC^2=AB^2+AC^2\)

\(\Rightarrow AC^2=BC^2-AB^2=25^2-20^2=225=15^2\Rightarrow AC=15cm\)

Áp dụng hệ thức lượng vào tam giác vuông ABC:

\(AB.AC=AH.BC\Rightarrow AH=\dfrac{AB.AC}{BC}=\dfrac{20.15}{25}=12cm\)

Xin lỗi tôi nhầm đấy.

1. A lot of cards have been sold during the season.

2. This switch shouldn't be touched.

3. Exercise won't be corrected by the teacher tomorrow.

4. Cloth puppets used to be made by her.

5. How many ways can this problem be solved?

6. This dress is used by me only on occasions.

7. Refreshments will be served.

8. A lot of work is going to be done by students.

9. My car can't be repaired by him.

10. A great deal of coffee is drunk in China.

1C

2A

1. ate

2. saw

3. heard

4. bought

5. went

6. made

7. flew

8. thought

1. went

2. had

3. wrote

4. was

5. slept

6. studied

7. taught 

8. tried

9. spends