= x.(x³ - 1).(x⁶ + x³ + 1) + x².(x³ - 1) + (x² + x + 1)

                   = (x² + x + 1). [x.(x -1).(x⁶ + x³ + 1) + x² + 1 ]

- Có 3 cách phát âm chính 
/t/: những từ có tận cùng : f , s , sh , ch , p , x , và những động từ có từ phát âm cuối là " s" 
Ví dụ: liked , stopped .... 

/id/: Những từ có tận cùng là : t, d 
Ví dụ: needed , wanted .... 

/d/: những trường hợp còn lại 
Ví dụ: lived , studied .

\(P=\left(5+5^2\right)+5^2\left(5+5^2\right)+....+5^{98}\left(5+5^2\right)=30\left(1+5^2+....+5^{98}\right)\) chia hết cho 30

=>P chia hết cho 30

=>đpcm

\(C=\frac{x^3}{x}+\frac{1000}{x}+\frac{1000}{x}=x^2+\frac{1000}{x}+\frac{1000}{x}\)

Vì x>0 nên \(\frac{1000}{x}\)>0

Áp dụng bất đẳng thức  Cauchy cho ba số dương . Ta có:

\(x^2+\frac{1000}{x}+\frac{1000}{x}\ge\sqrt[3]{x^2.\frac{1000}{x}.\frac{1000}{x}}=100\)

Dấu '=' xảy ra <=>\(x^2=\frac{1000}{x}\Leftrightarrow x^2.x=1000\Leftrightarrow x^3=1000\Leftrightarrow x=10\)

Vậy MIN_C=100 khi x=10

1. I knew Sarah was very busy, so I did not disturb her. (disturb)

2. I was very tired, so I left the party early. (leave)

3. The bed was very uncomfortable. I did not sleep very well. (sleep)

4. The window was open and a bird flew into the room. (fly)

5. The hotel wasn't very expensive. It did not cost very much. (cost)

6. I was in a hurry, so I  did not have time to phone you. (have)

7. It was hard carrying the bags. They were very heavy. (be)

2. I was very tired, so I left the party early. (leave)

3. The bed was very uncomfortable. I slept very well. (sleep)

4. The window was open and a bird flew into the room. (fly)

5. The hotel wasn't very expensive. It cost very much. (cost)

6. I was in a hurry, so I had time to phone you. (have)

7. It was hard carrying the bags. They were very heavy. (be)

1. I knew Sarah was very busy, so I disturbed her. (disturb)

2. I was very tired, so I left the party early. (leave)

3. The bed was very uncomfortable. I slept very well. (sleep)

4. The window was open and a bird flied into the room. (fly)

5. The hotel wasn't very expensive. It cost very much. (cost)

6. I was in a hurry, so I had time to phone you. (have)

7. It was hard carrying the bags. They were very heavy. (be)

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