\( 1)P = \dfrac{{\sqrt x }}{{\sqrt x + 3}} + \dfrac{{2\sqrt x }}{{\sqrt x - 3}} - \dfrac{{3x + 9}}{{x - 9}}\\ = \dfrac{{\sqrt x \left( {\sqrt x - 3} \right) + 2\sqrt x \left( {\sqrt x + 3} \right) - 3x - 9}}{{\left( {\sqrt x - 3} \right)\left( {\sqrt x + 3} \right)}}\\ = \dfrac{{3\sqrt x - 9}}{{\left( {\sqrt x - 3} \right)\left( {\sqrt x + 3} \right)}} = \dfrac{{3\left( {\sqrt x - 3} \right)}}{{\left( {\sqrt x - 3} \right)\left( {\sqrt x + 3} \right)}} = \dfrac{3}{{\sqrt x + 3}}\\ 2)P = \dfrac{1}{3} \Rightarrow \dfrac{3}{{\sqrt x + 3}} = \dfrac{1}{3} \Leftrightarrow \sqrt x + 3 = 9 \Leftrightarrow \sqrt x = 6 \Leftrightarrow x = 36\\ 3)\sqrt x \ge 0\forall x \Rightarrow \sqrt x + 3 \ge 3\forall x \Rightarrow \dfrac{3}{{\sqrt x + 3}} \le 1 \Rightarrow GTL{N_{\left( P \right)}} = 1 \Leftrightarrow x = 0 \)