$M = \dfrac{\sqrt x}{\sqrt x + 2}$
+) Với $x = 9$
$\Rightarrow \sqrt x = 3$
$\Rightarrow M = \dfrac{3}{3 + 2} = \dfrac{3}{5}$
+) Với $x = 4 + 2\sqrt3$
$\Rightarrow x = (\sqrt3 + 1)^2$
$\Rightarrow \sqrt x = \sqrt3 + 1$
$\Rightarrow M = \dfrac{\sqrt3 + 1}{\sqrt3 + 3}$
$\Rightarrow M = \dfrac{\sqrt 3 + 1}{\sqrt3(\sqrt3 + 1)}$
$\Rightarrow M = \dfrac{1}{\sqrt3} = \dfrac{\sqrt3}{3}$