I have an inexpensive ryobi miter saw that I bought just to do
straight chopping when I was making a lot of crates. I just butted the
cleats, and didn't really bother with miters. The saw table will
rotate 45 deg. in either direction, but the blade tilts 45 deg. in
only one direction (meaning it's not a so-called compound miter saw I
guess?)

I would like to do some baseboard molding. Nothing fancy, just 45 deg.
angles inside and outside.

So say, looking from the top down, the inside angle is going to look
like this /_________\ where the back edge line to the wall is exactly
six feet.

With one outside angle, it looks like this /___________/ where the
back edge point to front edge point is also six feet, and so on.

How do I apply the 1 to 1 square root formula (1.414) to a baseboard
that is, say 3 1/4 tall by 1 1/4 thick, to give me the exact over or
under six foot measurement at the angle? Or should I just be using
some kind of folding bevel or miter tool? Something cheap I can get at
the BORG? If so, what?