B

9. A

13. A

16. D

17. D

18. C

13. C

14. D

20. C

\(x^2+\dfrac{1}{x^2}=7\\ \\ \\ \\ \Rightarrow x^2+2x\cdot\dfrac{1}{x}+\dfrac{1}{x^2}=7+2x\cdot\dfrac{1}{x}=9\\ \\ \\ \\ \Rightarrow\left(x+\dfrac{1}{x}\right)^2=9\\ \\ \\ \\ \Rightarrow x+\dfrac{1}{x}=\pm3\)

Trường hợp 1: \(x+\dfrac{1}{x}=3\) ta có:

\(x^3+\dfrac{1}{x^3}=\left(x^2+\dfrac{1}{x^2}\right)\left(x+\dfrac{1}{x}\right)-\left(x+\dfrac{1}{x}\right)=7\cdot3-3=18\)

Trường hợp 2: \(x+\dfrac{1}{x}=-3\) ta có:

\(x^3+\dfrac{1}{x^3}=\left(x^2+\dfrac{1}{x^2}\right)\left(x+\dfrac{1}{x}\right)-\left(x+\dfrac{1}{x}\right)=7\cdot\left(-3\right)-\left(-3\right)=-18\)

1. C

2. B

3. A

4. A

5. B

6. C

Aesop

1. festive

2. performers

3. arguements

4. famous

5. musician

1. am driving

2. are / doing

3. are flying

4. aren't playing

5. is meeting

6. am not using

7. is leaving

8. Is / taking

9. isn't reading

10. Are / having

1. explorer

2. chemist

3. archaeologist

4. conservationist

5. physicist

6. software developer

7. biologist

8. inventor