\[\boxed{\mathbf{606\ (606).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ \sqrt{9 - 4\sqrt{5}} = \sqrt{4 - 4\sqrt{5} + 5} =\]
\[= \sqrt{\left( 2 - \sqrt{5} \right)^{2}} = \left| 2 - \sqrt{5} \right| =\]
\[= \sqrt{5} - 2\ \]
\[2)\ \sqrt{7 - 2\sqrt{10}} =\]
\[= \sqrt{5 - 2\sqrt{10} + 2} =\]
\[= \sqrt{\left( \sqrt{5} - \sqrt{2} \right)^{2}} = \left| \sqrt{5} - \sqrt{2} \right| =\]
\[= \sqrt{5} - \sqrt{2}\]
\[3)\ \sqrt{37 - 20\sqrt{3}} =\]
\[= \sqrt{25 - 10\sqrt{12} + 12} =\]
\[= \sqrt{\left( 5 - \sqrt{12} \right)^{2}} = \left| 5 - \sqrt{12} \right| =\]
\[= 5 - 2\sqrt{3}\]