cho A= 1/3+1/6+1/10+1/15+…+1/171+1/190 chứng tỏ ràng A<1

0 bình luận về “cho A= 1/3+1/6+1/10+1/15+…+1/171+1/190 chứng tỏ ràng A<1”

1. `A= 1/3 + 1/6 + 1/10 + 1/15+…+1/190`

   `1/2 A= 1/2(1/3 + 1/6 + 1/10+ 1/15+…+1/190)`

   `1/2 A= 1/6 + 1/12 + 1/20 + 1/30 +…+1/380`

   `1/2A = 1/2.3 + 1/3.4 + 1/4.5 + 1/5.6+…+1/19.20`

   `1/2A = 1/2 – 1/3 +1/3-1/4+1/4-….+1/19-1/20`

   `1/2 A = 1/2 – 1/20`

   `A= (1/2 – 1/20) : 1/2`

   `A= (1/2 – 1/20) . 2`

   `A= 1- 1/10 <1`

   Vậy `A<1`

    

   Bình luận