Đáp án:
`A=(1/(x-sqrtx)+1/(sqrtx-1)):(sqrtx+1)/(sqrtx-1)^2(x>0,x ne 1)`
`A=(1/(sqrtx(sqrtx-1))+sqrtx/(sqrtx(sqrtx-1)))*(sqrtx-1)^2/(sqrtx+1)`
`A=(sqrtx+1)/(sqrtx(sqrtx-1))*(sqrtx-1)^2/(sqrtx+1)`
`A=(sqrtx-1)/sqrtx`
`b)A=1/3`
`<=>(sqrtx-1)/sqrtx=1/3`
`<=>3(sqrtx-1)=sqrtx`
`<=>3sqrtx-3=sqrtx`
`<=>2sqrtx=3`
`<=>sqrtx=3/2`
`<=>x=9/4(tmđk)`
Vậy `x=9/4` thì `A=1/3.`
