`7)` Với `0 <= a \ne b` có:
`[a-b]/[\sqrt{a}-\sqrt{b}]=[(\sqrt{a}-\sqrt{b})(\sqrt{a}+\sqrt{b})]/[\sqrt{a}-\sqrt{b}]`
`=\sqrt{a}+\sqrt{b}`
`8)` Với `0 <= a,b` có:
`[a+b+2\sqrt{ab}]/[\sqrt{a}+\sqrt{b}]=[(\sqrt{a}+\sqrt{b})^2]/[\sqrt{a}+\sqrt{b}]`
`=\sqrt{a}+\sqrt{b}`