x²y²=xy(xy+xy)

xy=xy+xy

0=xy

=>xy=0(đpcm)

B=(1998-2)(1998+2)

=1998²-1998.2+1998.2-4

=1998²-4

=>A>B

B=(2000-10)(2000+10)

=2000²-10.2000+10.2000-10²

=2000²-10²

=>A>B

Hình như đề sai rồi

Ex1:

1) I visited Bana Hills last summer.

2) They went skiing 3 months ago.

3) Nam is doing homework at the moment.

Ex2:

1. I like the living room best in my house.

2.How about going to Sa Huynh Coffee tonight.

3.You mustn't talk too much in the class.

1.Longest

2.Bigger

3.Biggest

4.Taller

5.Older

6.Shorter.Shortest

7.Highest

8.Thicker

9.Longer