[tex] \bf \textit{area of an equilateral triangle}\\\\
A=\cfrac{s^2\sqrt{3}}{4}\qquad
s=side's~length
\\\\\\
4A=s^2\sqrt{3}\implies \cfrac{4A}{\sqrt{3}}=s^2\implies \sqrt{\cfrac{4A}{\sqrt{3}}}=s
\\\\\\
\stackrel{\textit{and if we rationalize the denominator}}{\sqrt{\cfrac{4A}{\sqrt{3}}\cdot \cfrac{\sqrt{3}}{\sqrt{3}}}\implies \sqrt{\cfrac{4A\sqrt{3}}{3}}} [/tex]