\[\sqrt{6 + 2\sqrt{5}} = 1 + \sqrt{5}\]
\[Возведем\ в\ квадрат:\]
\[\left( \sqrt{6 + 2\sqrt{5}} \right)^{2} = \left( 1 + \sqrt{5} \right)^{2}\]
\[6 + 2\sqrt{5} = 1 + 2\sqrt{5} + 5\]
\[6 + 2\sqrt{5} = 6 + 2\sqrt{5}\ \]
\[ч.т.д.\]