Cho ba số dương a,b,c<2. Chứng minh ít nhất một trong các bất đẳng thức sau là sai: a(2-b)>1; b(2-c)>1; c(2-a)>1.

(Gợi ý: Chứng minh bằng phương pháp phản chứng)

Write the correct form of the words given in capital letters:

1. Hoa is having a ................. check-up. MEDICINE

2. The nurse wanted to know Nga's height and .......... WEIGH

3. Edison's most famous .................... was the electronic bulb. INVENT

4. This dictionary is very .......... for you to learn English. USE

5. We must remember to eat .......... SENSE

6. Mr. Hung has a very .......... tooth. PAIN

7. She spent her .......... in the country. CHILD

8. The president is going to make a ........... tonight. SPEAK

Rewrite the following sentences with the meaning unchanged:

1. I am very pleased that we shall meet again soon.

--> I'm looking.................

2.I expect that he will get there by lunchtime.

--> I expect him............

3. I remember someone telling me the news.

--> I remember being...........

4. He didn't say goodbye to anyone when he left the room.

--> He left the room without...........

5. Asking him to help is useless.

--> It's no .............

6. We expect to help is useless.

--> We look............

Chứng minh: (ab+bc+ca)²\(\ge\)3abc(a+b+c)

Cho hai số x,y thỏa mãn ax+by=c; bx+cy=a; cx+ay=b. Chứng minh a³+b³+c³=3abc.