[tex]\dfrac{\sqrt x}{\sqrt x + \sqrt 5}\\\\\\\\= \dfrac{\sqrt x(\sqrt x - \sqrt 5)}{(\sqrt x + \sqrt 5)(\sqrt x - \sqrt 5)}\\\\\\= \dfrac{\left(\sqrt x \right)^2 - \sqrt{5x}}{\left(\sqrt x \right)^2 - \left(\sqrt 5)^2}}\\\\[/tex]
[tex]=\dfrac{x - \sqrt{5x}}{x -5}[/tex]
