Date: Sep 10, 2010 4:48 AM
Author: alan
Subject: Manipulating square roots

How can I get mathematica to bring a factor inside a square root?  For
instance
a Sqrt(1-(b/a)^2) -> Sqrt(a^2-b^2) (if a is real and a > 0).
Also, how do I get Mathematica to perform the operation in reverse?