Giải giúp mình với ạ

`(x>0;xne1)`

`a)A=((x-sqrtx)/(sqrtx-1)-(sqrtx+1)/(x+sqrtx)) :(sqrtx-1)/x`

`=((sqrtx(sqrtx-1))/(sqrtx-1)-(sqrtx+1)/(sqrtx(sqrtx+1))) .x/(sqrtx-1)`

`=(sqrtx-1/sqrtx) . x/(sqrtx-1)`

`=(sqrtxsqrtx-1)/sqrtx .x/(sqrtx-1)`

`=((sqrtx-1)(sqrtx+1)sqrtx)/(sqrtx-1)`

`=sqrtx(sqrtx+1)`

`=x+sqrtx`

`b)B=A-2sqrtx`

`=x+sqrtx-2sqrtx`

`=x-sqrtx`

`=x-2.sqrtx .1/2+1/4-1/4`

`=(sqrtx-1/2)^2-1/4`

Ta có `(sqrtx-1/2)^2>=0`

`<=>(sqrtx-1/2)^2-1/4>=-1/4`

`<=>B>=-1/4`

Dấu `'='` xảy ra`<=>sqrtx-1/2=0`

`<=>sqrtx=1/2`

`<=>x=1/4(tmđk)`

Vậy `min_B=-1/4<=>x=1/4`