\[\sqrt{14 - 2\sqrt{13}} =\]
\[= \sqrt{13 - 2\sqrt{13} + 1} =\]
\[= \sqrt{\left( \sqrt{13} - 1 \right)^{2}} = \left| \sqrt{13} - 1 \right| =\]
\[= \sqrt{13} - 1\]