a) đkxđ: `x>2`
`P=(x\sqrtx-8)/(x-4)-x/(\sqrtx+2)-4/(2-\sqrtx)`
`P=(x\sqrtx-8)/(x-4)-(x\sqrtx-2x)/(x-4)+(4\sqrtx+8)/(x-4)`
`P=(2x+4\sqrtx)/(x-4)`
b) `P=(2x+4\sqrtx)/(x-4)=\sqrtx+3`
`⇔(2x+4\sqrtx)/(x-4)=\sqrtx+3`
`⇔2x+4\sqrtx=(\sqrtx+3)(x-4)=3x+x\sqrtx-4\sqrtx-12`
`⇔x+x\sqrtx-8\sqrtx-12=0`
`⇔x=9`
Vậy `x=9`