Is there a way to find the discrete root?

Question

Mathematics

There is a strange formula in the article on Habré
Is there a quick way to find the root modulo? It seems that there is only a reduction to a discrete logarithm (and, moreover, only for a simple p) or a blunt enumeration. Or is it some kind of tricky operation, different from the accepted definition of the root modulo?

Answer 1

It is the square root in the annulus (in this case a field, since p is a prime number) of residue classes modulo p. About finding the root google://quadratic residue