I know this is a special case of a result that works in both directions for the nth root. But I'm trying to find a simple proof of this result.
Assume $gcd(p,q)=1$ and $\sqrt k=\frac{p}{q}$, so $k = \frac{pp}{qq}$ and $qqk=pp$ ---> Then some fundamental theorem of arithmetic magic comes next or something.
Any help would be appreciated