7 ____ 2√21 Решите пожалуйста!!!

[latex] \frac{7}{2 \sqrt{21} }= \frac{7*\sqrt{21}}{2\sqrt{21}*\sqrt{21}} = \frac{7\sqrt{21}}{2*21}= \frac{7\sqrt{21}}{42}= \frac{\sqrt{21}}{6}[/latex]