Please take a look here:
http://www.truevision3d.com/tvdna/source/classes/tvmathlibrary.htmWhile it is documentation for TV3D 6.1, a lot of those functions exist in 6.5 (assuming you are using 6.5), plus 6.5 has added lots of new stuff. If your IDE has an object browser it would be good to take a look and see what is available.
There are functions for adding together 2D, 3D and 4D vectors plus lots of other vector manipulation functions.