A, CHO A, B, C ≠ 02 2 2A B C A B C2 2 2B  C  A   B C A CMR

Câu 2:

a, Cho a, b, c ≠ 0

2

2

2

a b c a b c

b  c  a   b c a 

CMR:

b, Cho n ^ N, n > 1

1 1 1 1

5 13   ....  n n ( 1)  2



CMR:

²

²