Create your triangle first, with the right dimensions, and then go to Effect>Stylize>Round Corners. Easy as pie.
This method is great if you want the inner and outer angles all rounded. But if you want only the points of the triangle rounded, then you'll need to do this:
Erm, WHATTTTT?????? That makes no sense.
Thank you very muchCreate your triangle first, with the right dimensions, and then go to Effect>Stylize>Round Corners. Easy as pie.