$(x\ge 0;x\ne 1)$
Ta có:
`VT=(3-{x+\sqrt{x}}/{\sqrt{x}+1})(3+{x-\sqrt{x}}/{\sqrt{x}-1})`
`=[3-{\sqrt{x}(\sqrt{x}+1)}/{\sqrt{x}+1}][3+{\sqrt{x}(\sqrt{x}-1)}/{\sqrt{x}-1}]`
`=(3-\sqrt{x})(3+\sqrt{x})`
`=3^2-(\sqrt{x})^2`
`=9-x=VP`
Vậy:`(3-{x+\sqrt{x}}/{\sqrt{x}+1})(3+{x-\sqrt{x}}/{\sqrt{x}-1})=9-x`