Choice exact-sqrt

While taking square roots is an inexact operation in general, the answer can be represented exactly in some cases. For instance, the mathematical square root of nine is exactly three. Then (sqrt 9) could be an exact three, or it could be an inexact three on the logic that sqrt will have to return inexact results given exact arguments in other cases.

This choice is tested for by running

(exact? (sqrt 9))

in each Scheme.