Question

Chung to :1/2 + 1/3 + 1/4 +...+1/9 <2

Answer 1

Đặt A=1/2+1/3+1/4+...+1/9

       A=(1/2+1/3)+(1/4+1/5)+(1/6+1/7)+(1/8+1/9)

       A<1/2+1/3+1/4+1/4+1/6+1/6+1/8+1/8

      A<5/6+1/2+1/3+1/4

      A<23/12<24/12=2

Nên A<2