Square root symbol! How'd you do that?!
Back in the early days of ASCII only, the typical character set was 2^8 = 256 characters, of which only a subset was available on the keyboard. Hence the system set up the ability to put the other characters in by odd means and devious.
These days, the easiest way (in Windows) is to run the charmap program - see the previous post for the location. This little utility allows you to copy and paste any character into your application, including a bunch of math symbols. I don't know what, if any, is the limit these days but the sets have heaps and heaps of characters.