This really does not have that much to do with programming, but
I didn't want to have to post it in a math forum, and I thought
this would kind of relate to 3D graphics.
I want to know what determines whether or not a plane is visible
from a certain vantage point. I know that when I take a piece of paper
and rotate it far enough, one side of the paper becomes invisible.
It's kind of like when a polygon becomes invisible on one side.