Ahijhij! Help me

Question

Chứng tỏ rằng : 

                         D = 1/2^2 + 1/3^2 + 1/4^2 + .... + 1/10^2

Answer 1

    D = 1/2^2 + 1/3^2 + 1/4^2 + .... + 1/10^2 < 1/1.2 + 1/2.3 + 1/3.4 + .... + 1/9.10

       = 1 - 1/2 + 1/2 - 1/3 + ... + 1/9 - 1/10

       = 1 - 1/10 = 9/10 < 1

Answer 2

D=1/2.2+1/3.3+1/4.4+...+1/10.10

D

Answer 3

  D = 1/2^2 + 1/3^2 + 1/4^2 + .... + 1/10^2 < 1/1.2 + 1/2.3 + 1/3.4 + .... + 1/9.10

       = 1 - 1/2 + 1/2 - 1/3 + ... + 1/9 - 1/10

       = 1 - 1/10 = 9/10 < 1

bn nhé