ko ai trả lời thì để mình

C/M : n/n+1 < n+1/n+2

1 - n/n+1 = 1/n+1

1 - n/n + 2 = 1/n+2

Vì 1/n+1 > 1/n+2 nên n/n+1 < n+1/n+2

1/2 . 3/4 . 5/6 ... 2499/2500 < 1/2 . 2/3 . 3/4 ... 2501/2502

=1/2501 < 1/2500 (1/50) ²

1/50 < 1/49 => A <1/49