\[\sqrt{\left( \sqrt{5} - 4 \right)^{2}} - \sqrt{\left( \sqrt{5} - 2 \right)^{2}} =\]
\[= \left| \sqrt{5} - 4 \right| - \left| \sqrt{5} - 2 \right| =\]
\[= 4 - \sqrt{5} - \left( \sqrt{5} - 2 \right) =\]
\[= 4 - \sqrt{5} - \sqrt{5} + 2 = 6 - 2\sqrt{5}\]