Đáp án:
\(\dfrac{5}{{\sqrt x + 3}}\)
Giải thích các bước giải:
\(\begin{array}{l}
A = \left[ {\dfrac{{\left( {\sqrt x - 5} \right)\sqrt x }}{{\left( {\sqrt x - 5} \right)\left( {\sqrt x + 5} \right)}} - 1} \right]:\dfrac{{25 - x - \left( {\sqrt x - 3} \right)\left( {\sqrt x + 3} \right) + \left( {\sqrt x - 5} \right)\left( {\sqrt x + 5} \right)}}{{\left( {\sqrt x + 5} \right)\left( {\sqrt x - 3} \right)}}\\
= \dfrac{{\sqrt x - \sqrt x - 5}}{{\sqrt x + 5}}.\dfrac{{\left( {\sqrt x + 5} \right)\left( {\sqrt x - 3} \right)}}{{25 - x - x + 9 + x - 25}}\\
= \dfrac{{ - 5}}{{\sqrt x + 5}}.\dfrac{{\left( {\sqrt x + 5} \right)\left( {\sqrt x - 3} \right)}}{{ - x + 9}}\\
= \dfrac{{5\left( {\sqrt x - 3} \right)}}{{\left( {\sqrt x - 3} \right)\left( {\sqrt x + 3} \right)}} = \dfrac{5}{{\sqrt x + 3}}
\end{array}\)
