Projection Distance

There are some silly rules and mathematics in photography, here is a theoric base for setting up the distance for projection, as can be used for exhibition and flatscreen.

If L is the wideness of the projected area, then the first viewers has to sit at 3 times this measurement and the last one at 4,5 times this distance.

Not practical, cannot be used in cinemas and I think when I play the last version of my favorite killing game on my Playstation 3 on my 42 inch flatscreen, I would be complete out of the game.