Geometry

There's a pretty handy formula to find the circumradius of a triangle. 

We have $\frac{(abc)}{\sqrt{(a + b + c)(b + c - a)(c + a - b)(a + b - c)}}$ where a, b, and c are the sidelegnths. 

Here, we just have $\frac{a^3}{\sqrt{3a^4}} = \frac{a^3}{a^2 \cdot \sqrt3}= \frac{a}{\sqrt{3}}$. 

So $\frac{a}{\sqrt3}$ is our answer. 

Thank You! :)

This was the post that got me to 300 points LOL :)