Answer:
I assume your goal is to rationalize the denominator -
So you need to multiply the denominator by its conjugate.
So we have:
[tex]\frac{\sqrt{x} }{\sqrt{x}-\sqrt{7} } *\frac{\sqrt{x} +\sqrt{7} }{\sqrt{x} +\sqrt{7}}[/tex]
->
[tex]\frac{x-\sqrt{7}\sqrt{x} }{x-7}[/tex]
gg