cos2x + cosx + 1 = 0

<=> 2cos^2 (x) - 1 - cosx + 1 = 0 

<=> 2cos^2 (x) - cosx = 0 

<=> cosx = 1/2 hoặc cosx = 0 

<=> x = +- π/3 + k2π  hoặc x = π/2 + kπ

I = q/t -> q = I.t = 1,5.3 = 4,5C

Em sẽ khuyên và ngăn chặn những hành động sai đó của bạn. Nếu còn tiếp diễn em sẽ báo lại với thầy cô chủ nhiệm để có thể xử lí những trường hợp như vậy

B. apart for

1. If we use cars all the time, we will make the air dirty.

2. He has a lot of time tomorrow so he will be able to see a movie

1. interesting

2. entrance

3. hilly

4. enjoyable

5. enjoyably

6. beautifully 

7. arrived

8. parking 

9. groceries

10. nearby

11. exchange

12. collection

13. mountainous

14. uninteresting

15. interesting

16. picnic

17. surprisingly

18. flight

19. enter

III

1.a

2.b

3.c

4.a

5.b

6.a

7.b

8.c

9.a

10.d

25. D

26. D

27. C

28. A

29. B

30. D

31. D

32. B

High-rise buildings coming up close, the transportation system and infrastructure has developed dramatically, social security is increasingly focused, children's education is also improved, our people see life Less suffering than before, more comfortable than before, new roads help people travel more conveniently.