\(\begin{array}{l} DK:x \ge 0;x \ne 25\\ A = \frac{{5 + \sqrt x }}{{x - 25}}.\frac{{\sqrt x - 5}}{{\sqrt x + 1}}\\ = \frac{{5 + \sqrt x }}{{\left( {5 + \sqrt x } \right)\left( {\sqrt x - 5} \right)}}.\frac{{\sqrt x - 5}}{{\sqrt x + 1}}\\ = \frac{1}{{\sqrt x + 1}} \end{array}\)
