Question

[Khiếu Việt Bách]

Chứng minh

A)H=1/2<1/51+1/52+1/53+...+1/100<1

B)7/12<1/21+1/22+1/23+...+1/40<5/6

C)1<S<2 biết: S=6/15+6/16+6/17+...+6/19

Answer 1

[Khổng Mai Linh]

a,1/51 > 1/100

  1/52 > 1/100

   1/53 > 1/100

    ...

     1/100=1/100

=>H>1/100 + 1/100 + 1/100 +...+1/100

    H>50/100=1/2   

          1/51<1/50

         1/52<1/50

           ....

           1/100<1/50

=>H<1/50+1/50+...+1/50

     H<50/50=1

 Vay1/2<H<1