\[x^{2} = \left( \sqrt{5} - 2 \right)\sqrt{9 + 4\sqrt{5}}\]
\[\sqrt{9 + 4\sqrt{5}} = \sqrt{5 + 4\sqrt{5} + 4} = \sqrt{\left( \sqrt{5} + 2 \right)^{2}} = \sqrt{5} + 2;\]
\[\left( \sqrt{5} - 2 \right)\left( \sqrt{5} + 2 \right) = 5 - 4 = 1;\]
\[x^{2} = 1\]
\[x = \pm 1.\]
\[Ответ:x = \pm 1.\]