Đáp án:
`a)P=((\sqrtx+2)/(sqrtx-2)-(sqrtx-2)/(sqrtx+2)-(4x)/(4-x)):(x+5sqrtx+6)/(x-4)`
`P=((sqrtx+2)^2-(sqrtx-2)^2+4x)/(x-4):((sqrtx+2)(sqrtx+3))/((sqrtx-2)(sqrtx+2))`
`P=((4x+8sqrtx)/(x-4)):(sqrtx+3)/(sqrtx-2)`
`P=(4sqrtx(sqrtx+2))/((sqrtx-2)(sqrtx+2))*(sqrtx-2)/(sqrtx+3)`
`P=(4sqrtx)/(sqrtx+3)`
`b)x=sqrt{9+4sqrt5}-sqrt{9-4sqrt5}`
`x=sqrt{5+2.2.sqrt5+4}-sqrt{5-2.2.sqrt5+4}`
`x=sqrt{(sqrt5+2)^2}-sqrt{(sqrt5-2)^2}`
`x=sqrt5+2-sqrt5+2=4`
`=>P=(4.2)/(2+3)=8/5`
`c)P=2`
`<=>(4sqrtx)/(sqrtx+3)=2`
`<=>(2sqrtx)/(sqrtx+3)=1`
`<=>2sqrtx=sqrtx+3`
`<=>sqrtx=3`
`<=>x=9(tmđk)`
Vậy `x=9` thì `P=2`.
