`ĐK:` `a>=0,ane1,ane4`
`(1/(\sqrt{a}-1)-1/\sqrt{a}):((\sqrt{a}+1)/(\sqrt{a}-2)-(\sqrt{a}+2)/(\sqrt{a}-1))`
`=(\sqrt{a}-\sqrt{a}+1)/(\sqrt{a}(\sqrt{a}-1)):((\sqrt{a}+1)(\sqrt{a}-1)-(\sqrt{a}+2)(\sqrt{a}-2))/((\sqrt{a}-2)(\sqrt{a}-1))`
`=(1)/(\sqrt{a}(\sqrt{a}-1)):(a-1-a+4)/((\sqrt{a}-2)(\sqrt{a}-1))`
`=(1)/(\sqrt{a}(\sqrt{a}-1)):(3)/((\sqrt{a}-2)(\sqrt{a}-1))`
`=(1)/(\sqrt{a}(\sqrt{a}-1)).((\sqrt{a}-2)(\sqrt{a}-1))/(3)`
`=(\sqrt{a}-2)/(3\sqrt{a})`
`=(\sqrt{a}(\sqrt{a}-2))/(3\sqrt{a}\sqrt{a})`
`=(a-2\sqrt{a})/(3a)`
