\[= \sqrt{\left( \sqrt{a} - 6 \right)^{2}} + \sqrt{\left( \sqrt{a} + 7 \right)^{2}} =\]
\[= \left| \sqrt{a} - 6 \right| + \sqrt{a} + 7\]
\[При\ a \geq 6:\]
\[\sqrt{a} - 6 + \sqrt{a} + 7 = 2\sqrt{a} + 1.\]
\[При\ a < 6:\]
\[6 - \sqrt{a} + \sqrt{a} + 7 = 13.\]