[tex]\displaystyle
\frac{ \sqrt{6}- \sqrt{3}-\sqrt{2}+1}{\sqrt{10}- \sqrt{5}+\sqrt{2}-1} = \\ \\ \\
=\frac{ (\sqrt{3\times2}- \sqrt{3})-(\sqrt{2}-1)}{(\sqrt{5\times2}- \sqrt{5})+(\sqrt{2}-1)} = \\ \\ \\
=\frac{ \sqrt{3}(\sqrt{2}- 1)-(\sqrt{2}-1)}{ \sqrt{5}(\sqrt{2}- 1)+(\sqrt{2}-1)} = \\ \\ \\
=\frac{ (\sqrt{2}- 1)(\sqrt{3}-1)}{ (\sqrt{2}- 1)(\sqrt{5}+1)} = ~~~se~simplifica~prin~(\sqrt{2}- 1) \\ \\ \\ =\boxed{\frac{ \sqrt{3}-1}{ \sqrt{5}+1}}[/tex]