To rewrite 812 using a root, you can express it as \( \sqrt{812^2} \) since taking the square root of the square of a number returns the original number.
However, among the given options, none seem to effectively represent 812 using a root in a straightforward manner.
If you're looking for a way to perhaps break down 812 in relation to its prime factorization or any other simplifying root representation, the question as asked may not have a clear correct option based on standard mathematical conventions.
Please clarify if you're looking for a different kind of representation!