Giúp vs ahhhhhhhhhhhh

Ta có:`A=9/1+8/2+7/3+...+1/9`

Và `B=1/2+1/3+1/4+...+1/10`

`=>A/B=(9/1+8/2+7/3+...+1/9)/(1/2+1/3+1/4+...+1/10)`

`=>A/B=(9+8/2+7/3+...+1/9)/(1/2+1/3+1/4+...+1/10)`

`=>A/B=((1+8/2)+(1+7/3)+...+(1+1/9)+1)/(1/2+1/3+1/4+...+1/10)`

`=>A/B=(10/2+10/3+...+10/9+10/10)/(1/2+1/3+1/4+...+1/10)`

`=>A/B=(10.(1/2+1/3+...+1/9+1/10))/(1/2+1/3+1/4+...+1/10)`

`=>A/B=10`

Thay `A/B` vào `(A/Bx-1)^2=1` ta được:

`(10x-1)^2=1`

`=>(10x-1)^2=(+-1)^2`

`=>[(10x-1=1),(10x-1=-1):}`

`=>[(10x=2),(10x=0):}`

`=>[(x=1/5),(x=0):}`

Vậy `x in {1/5;0}`