a)    Cho S = 1.2.3 + 2.3.4 + 3.4.5 + . . . + k(k+1)(k+2)

           Chứng minh rằng 4S + 1 là số chính phương .

Cho hình chữ nhật ABCD. Gọi H là chân đường vuông góc kẻ từ A xuống BD. Gọi M , N lần lượt là trung điểm của BH; CD.

Chứng minh rằng: AM vuông góc với MN

đúng chọn T, sai chọn F

In the 1960s, The Beatles were probably the most famous pop group in the whole world. Since then, there have been a great many groups that have achieved enormous fame, so it is perhaps difficult now to imagine how sensational The Beatles were at that time. They were four boys from the north of England and none of them had any training in music.They started by performing and recording songs by black Americans and they had some success with these songs. Then they started writing their own songs and that was when they became really popular.The Beatles changed pop music.They were the first pop group to achieve great success from songs they had writen themselves. After that it became common for groups and singers to write their own songs. The Beatles did not have a long career. Their first hit record was in 1963 and they split up in 1970. They stopped doing live performances in 1966 because it had become too dangerous for them – their fans were so excited that they surrounded them and tried to take their clothes as souvenirs! However, today some of their songs remain as famous as they were when they first came out. Throughout the world many people can sing part of a Beatles song if you ask them.

1. prior to the beatles, it was usual tor groups to write their own songs

2. the beatles were the most famous pop group in the 1906s

3. the beatles did not succeed with the song by black americans

4. some members of the beatles studied music at school

5. the beatles achieved great success with the song they had written