Giải thích các bước giải:
Ta có:
\(\begin{array}{l}
a,\\
P = \left( {\dfrac{{\sqrt x }}{{\sqrt x - 2}} + \dfrac{{\sqrt x }}{{\sqrt x + 2}}} \right).\dfrac{{x - 4}}{{\sqrt {4x} }}\\
= \dfrac{{\sqrt x .\left( {\sqrt x + 2} \right) + \sqrt x .\left( {\sqrt x - 2} \right)}}{{\left( {\sqrt x - 2} \right)\left( {\sqrt x + 2} \right)}}.\dfrac{{x - 4}}{{\sqrt 4 .\sqrt x }}\\
= \dfrac{{x + 2\sqrt x + x - 2\sqrt x }}{{{{\sqrt x }^2} - {2^2}}}.\dfrac{{x - 4}}{{2\sqrt x }}\\
= \dfrac{{2x}}{{x - 4}}.\dfrac{{x - 4}}{{2\sqrt x }}\\
= \dfrac{x}{{\sqrt x }} = \sqrt x \\
b,\\
P > 3 \Leftrightarrow \sqrt x > 3 \Leftrightarrow x > 9
\end{array}\)
