Question

giúp mik  câu b với bài 3 ạ

 

Answer 1

3:

A=1-1/2+1/3-1/4+...+1/99-1/100

=1/51+1/52+...+1/100

=(1/51+1/52+...+1/75)+(1/76+1/77+...+1/100)

1/51+1/52+...+1/75>25/75=1/3

1/76+1/77+...+1/100>25/100=1/4

=>A>7/12

1/51+1/52+...+1/75<25/50=1/2

1/76+1/77+...+1/100<25/75=1/3

=>A<5/6

=>7/12<A<5/6