Consider $x^2=[2]\_7$ where $[2]\_7$ is the congruence class of $a$ modulo $m$, or
$$[2]\_7=\{x\in\mathbb{Z} \ | x\equiv 2 \ (\text{mod} \ 7)\}.$$
It is immediately obvious, by inspection, that $x=[3]\_7$ and $x=[4]\_7$, but is there any way to analytically attain these solutions?