`3, P= A/B`

`=2/(sqrtx -2) : (sqrtx+2)/(sqrtx -2 )`

`=2/(sqrtx -2) . (sqrtx-2)/(sqrtx +2 )`

`=2/(sqrtx +2 )`

`P >= 2/(x+2)`

`<=> 2/(sqrtx +2 ) >= 2/(x+2)`

`<=> sqrtx +2  <= x+2`

`<=>x -sqrtx >= 0`

`<=>sqrtx(sqrtx-1) >= 0`

`<=>sqrtx-1>=0(text( vì) sqrtx >=0)`

`<=>sqrtx>=1`

`<=>x>=1`

Kêt hợp với điều kiện `=> 1 <= x ne 4`

Vậy `1 <= x ne 4`