\[\boxed{\text{885\ (885).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ \sqrt{19 - 6\sqrt{10}} = \sqrt{10} - 3\]
\[\sqrt{19 - 6\sqrt{10}} = \sqrt{10} - 3\]
\[\sqrt{10 - 2 \cdot 3\sqrt{10} + 9} = \sqrt{10} - 3\]
\[\sqrt{\left( \sqrt{10} - 3 \right)^{2}} = \sqrt{10} - 3\]
\[\sqrt{10} - 3 = \sqrt{10} - 3.\]
\[\textbf{б)}\ \sqrt{23 - 8\sqrt{7}} = 4 - \sqrt{7}\]
\[\sqrt{23 - 8\sqrt{7}} = 4 - \sqrt{7}\]
\[\sqrt{16 - 2 \cdot 4\sqrt{7} + 7} = 4 - \sqrt{7}\]
\[\sqrt{\left( 4 - \sqrt{7} \right)^{2}} = 4 - \sqrt{7}\]
\[4 - \sqrt{7} = 4 - \sqrt{7}.\]