`a)`

`A=sqrt{2}(sqrt{2-sqrt{3}}+sqrt{2})-sqrt{3}`

`A=sqrt{2(2-sqrt{3})}+2-sqrt{3}`

`A=sqrt{4-2sqrt{3}}+2-sqrt{3}`

`A=sqrt{3-2sqrt{3}+1}+2-sqrt{3}`

`A=sqrt{(sqrt{3}-1)^2}+2-sqrt{3}`

`A=|sqrt{3}-1|+2-sqrt{3}`

`A=sqrt{3}-1+2-sqrt{3}`

`A=1`

`B=(xsqrt{x})/(x-sqrt{x})-(2sqrt{x}-1)/(sqrt{x}-1) (x>0;x ne 1)`

`B=(xsqrt{x})/(sqrt{x}(sqrt{x}-1))-(2sqrt{x}-1)/(sqrt{x}-1)`

`B=x/(sqrt{x}-1)-(2sqrt{x}-1)/(sqrt{x}-1)`

`B=(x-2sqrt{x}+1)/(sqrt{x}-1)`

`B=((sqrt{x}-1)^2)/(sqrt{x}-1)`

`B=sqrt{x}-1`

`b)`

Để `B>=A-1` thì

`sqrt{x}-1>=1-1`

`sqrt{x}-1>=0`

`sqrt{x}>=1`

`x>=1`

Mà `x ne 1=>x>1`

Vậy `x>1`