What is the set of numbers to which #sqrt(82/20)# belong?
Being a radical (root) expression, it would at first belong to the set of irrational numbers.
We could see if things can be taken out from under the radical sign:
But that's about all.
It is an irrational number, which is a subset of the real numbers.
("irrational" meaning that the number cam't be written as a fraction).