Tìm x biết:
a)3.(x-2)+2.(x-3)=5
b)(2x-8)²-16=0
c)(2x-1)²-(4x+1).(x-3)=3

Tính:
a) 3.(2x-3)+5.(x+2)
b) 3x.(2x-8)+(6x-2).(5-x)
c) (x-3).(x+3)-(x-5)² 
d) (x-y)³-(x-y).(x²+xy+y²)

Hãy so sánh phân tử khí oxi nặng hay nhẹ hơn,bằng bao nhiêu lần so với:
a)Phân tử khí cacbonic (1C,2O)
b)Phân tử khí lưu huỳnh đioxit (1S,2O)
c)Phân tử khí amoniac (1N,3H)

Hãy so sánh phân tử khí oxi nặng hay nhẹ hơn,bằng bao nhiêu lần so với:
a)Phân tử khí cacbonic (1C,2O)
b)Phân tử khí lưu huỳnh đioxit (1S,2O)
c)Phân tử khí amoniac (1N,3H)

Fill in the blank with correct reflexive pronouns 

1. Both boys taught ______ to swim.   

2. The children are amusing ______ with the small cat. 

3. We enjoyed ______ very much last night.   

4. The little girl hurt ______ when she fell.   

5. She looked at ______ in the mirror.   

6. Did you enjoy ______ at the party last night?  

7. She dressed ______.   

8. The children are not old enough to dress ______.   

9. My father cut ______ this morning when he was shaving.   

10. The boy taught ______ to speak French.