1. " I suggest going to Hanoi at the weekend." - " ...."

A. That's a fine day

B. That's a good idea

C. That's a good trip

D. That's a reason

2. I haven't finished packing my suitcase yet. - ...

A. I'll take you on holiday

B. When did it happen?

C. Well, hurry up then

*Choose the correct answer:

1, Let's go to Hanoi tomorrow.

A. What a pity! B. OK. Why not?

2. When does the next leave?

A. Yesterday B. In 10 minutes C. From platform 4

3. They walked for 2 hours until they .... to the river.

A. arrived B. came C. crossed

4. The reason .... the accident was that he drove too fast.

A. of B. why C. for D. by

5. How long ..... you (wait) ..... for me ?

6. There is a river .... across the village.

A. flowing B. running C. lying D. reaching

(y-\(\dfrac{1}{2}\)) : (\(\dfrac{1}{2}\)+\(\dfrac{1}{6}\)+\(\dfrac{1}{12}\)+\(\dfrac{1}{20}\)+....+\(\dfrac{1}{90}\))=\(\dfrac{1}{6}\)

Tổng của 3 số A; B; C là 223,998. Nếu chuyển dấu phẩy của A sang trái 1 hàng thì được B.Nếu chuyển dấu phẩy của A sang phải thì được C. Tìm 3 số đó.

 3/5 nhân 3/5 nhân 3,14

\(\frac{3}{5}.\frac{3}{5}.3,14=\frac{1413}{1250}\)

ta sử dụng bđt \(\frac{1}{a}+\frac{1}{b}\ge\frac{4}{a+b}\)(cái này bạn có thể dễ dàng chúng minh )

ta có 

\(\frac{1}{p-a}+\frac{1}{p-b}\ge\frac{4}{p-a+p-b}=\frac{4}{2p-\left(a+b\right)}=\frac{4}{c}\)(1)

tương tự ta có 

\(\frac{1}{p-b}+\frac{1}{p-c}\ge\frac{4}{a}\) (2)

\(\frac{1}{p-c}+\frac{1}{p-a}\ge\frac{4}{b}\)(3)

cộng theo vế của bđt (1);(2);(3) ta có

\(2\left(\frac{1}{p-a}+\frac{1}{p-b}+\frac{1}{p-c}\right)\ge4\left(\frac{1}{a}+\frac{1}{b}+\frac{1}{c}\right)\)

hay \(\frac{1}{p-a}+\frac{1}{p-b}+\frac{1}{p-c}\ge2\left(\frac{1}{a}+\frac{1}{b}+\frac{1}{c}\right)\)