\frac{2}{\sqrt6-\sqrt3}
\frac{2}{\sqrt6-\sqrt3}=\frac{2}{\sqrt6-\sqrt3}*\frac{\sqrt6+\sqrt3}{\sqrt6+\sqrt3}=
=\frac{2\sqrt6+2\sqrt3}{6-3}=\frac{2\sqrt6-2\sqrt3}{3}