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Đáp án:

`a.`Rút gọn `Q`:
`Q=sqrtx/(sqrtx-1)-2/(sqrtx+1)-2/(x-1)`
    `=sqrtx/(sqrtx-1)-2/(sqrtx+1)-2/((sqrtx-1)(sqrtx+1))`
    `=(sqrtx(sqrtx+1)-2(sqrtx-1)-2)/((sqrtx-1)(sqrtx+1))`
    `=(x+sqrtx-2sqrtx+2-2)/((sqrtx-1)(sqrtx+1))`
    `=(x-sqrtx)/((sqrtx-1)(sqrtx+1))`
    `=(sqrtx(sqrtx-1))/((sqrtx-1)(sqrtx+1))`
    `=sqrtx/(sqrtx+1)`
`b.`Tính giá trị `Q`:
Với `x=9` (tmdkxd) thì `Q=sqrt9/(sqrt9+1)=3/(3+1)=3/4`
Vậy `Q=3/4` khi `x=9`