so sánh A=1/2.9+1/3.12+1/4.15+1/5.18+...+1/2020.6063 với 1/6

Đáp án:

`A<1/6`

Giải thích các bước giải:

`A=1/2.9+1/3.12+1/4.15+1/5.18+...+1/2020.6063`

`3A=(1.3)/2.9+(1.3)/3.12+(1.3)/(4.15)+(1.3)/5.18+...+(1.3)/2020.6063`

`3A=1/2.3+1/3.4+1/4.5+1/5.6+...+1/2020.2021`

`3A=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+...+1/2020-1/2021`

`3A=1/2-1/2021`

`3A=2019/4042`

`A=2019/4042:3`

`A=673/4042`

`A=673/4042<673/4038=1/6`

Vậy `A<1/6`.