Với `x > 0,x \ne 1,x \ne 4` có:
`(1/[\sqrt{x}-1]-1/\sqrt{x}):([\sqrt{x}+1]/[\sqrt{x}-2]-[\sqrt{x}+2]/[\sqrt{x}-1])`
`=[\sqrt{x}-\sqrt{x}+1]/[\sqrt{x}(\sqrt{x}-1)]:[(\sqrt{x}-1)(\sqrt{x}+1)-(\sqrt{x}+2)(\sqrt{x}-2)]/[(\sqrt{x}-2)(\sqrt{x}-1)]`
`=1/[\sqrt{x}(\sqrt{x}-1)].[(\sqrt{x}-2)(\sqrt{x}-1)]/[x-1-x+4]`
`=[\sqrt{x}-2]/[3\sqrt{x}]`
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