- Find some motivations.

- Think about the reward when you overcame it.

- Seek help.

*If just a normal "big rock", just cry and then keep moving forward, no one will make fun of that !!!

Đặt `x^2=t (t>=0)`, có:

`2t^2+5t+2=0`

`\Delta = 5^2-4.2.2=9>0`

`=>` PT có 2 nghiệm:

`t_1=-1/2 (KTM)`

`t_2=-2 (KTM)`

Vậy PTVN.

- Sai cmnr. =(((

`(1/243)^9 = [1/(3^5)]^9 = [(1/3)^5]^9=(1/3)^13`

Vì: `1/3 > 1/83`

`=> (1/3)^13 > 1/(83)^13`.

1. Vì stiren có liên kết đôi, kém bền, dễ phá vỡ nên dễ phản ứng.

2. 

`C_6 H_5 - CH = CH2 + Br_2 → C_2 H_5 - CH(Br) - CH_2 (Br)`

`3C_6 H_5 - CH = CH2 + 2KMnO_4 + 4H_2O → C_6 H_5 - CH (OH) - CH_2 (OH) + 2MnO_2 + 2KOH`

- Trái nghĩa tươi mát: khô héo, úa tàn,..

a) More trees will be planted along this street by us.

b) In spite of their height, they still love playing sport.

c) Solar energy will be used to solve the problem of the energy shortage.

19. seasonal

`x>= 0 => A = 5x-1-3x=2x-1`

`x<0 => A=5x-1+3x=8x-1`

1. D

2. A

3. B

4. D

5. A

6. C

7. D

8. B

9. A

10. C

11. B

12. C

13. B

14. A

15. D