\[A = \frac{{\sqrt x }}{{\sqrt x - 5}} - \frac{{10\sqrt x }}{{x - 25}} - \frac{5}{{\sqrt x + 5}}\] (x ≥ 0; x ¹ 25)

\[ = \frac{{\sqrt x }}{{\sqrt x - 5}} - \frac{{10\sqrt x }}{{\left( {\sqrt x - 5} \right)\left( {\sqrt x + 5} \right)}} - \frac{5}{{\sqrt x + 5}}\]

\[ = \frac{{\sqrt x \left( {\sqrt x + 5} \right)}}{{\left( {\sqrt x - 5} \right)\left( {\sqrt x + 5} \right)}} - \frac{{10\sqrt x }}{{\left( {\sqrt x - 5} \right)\left( {\sqrt x + 5} \right)}} - \frac{{5\left( {\sqrt x - 5} \right)}}{{\left( {\sqrt x - 5} \right)\left( {\sqrt x + 5} \right)}}\]

\[ = \frac{{\sqrt x \left( {\sqrt x + 5} \right) - 10\sqrt x - 5\left( {\sqrt x - 5} \right)}}{{\left( {\sqrt x - 5} \right)\left( {\sqrt x + 5} \right)}}\]

\[ = \frac{{x + 5\sqrt x - 10\sqrt x - 5\sqrt x + 25}}{{\left( {\sqrt x - 5} \right)\left( {\sqrt x + 5} \right)}}\]\[ = \frac{{x - 10\sqrt x + 25}}{{\left( {\sqrt x - 5} \right)\left( {\sqrt x + 5} \right)}}\]

\[ = \frac{{{{\left( {\sqrt x - 5} \right)}^2}}}{{\left( {\sqrt x - 5} \right)\left( {\sqrt x + 5} \right)}} = \frac{{\sqrt x - 5}}{{\sqrt x + 5}}\].

Vậy \[A = \frac{{\sqrt x - 5}}{{\sqrt x + 5}}\].