The page you are reading is part of a draft (v2.0) of the "No bullshit guide to math and physics."
The text has since gone through many edits and is now available in print and electronic format. The current edition of the book is v4.0, which is a substantial improvement in terms of content and language (I hired a professional editor) from the draft version.
I'm leaving the old wiki content up for the time being, but I highly engourage you to check out the finished book. You can check out an extended preview here (PDF, 106 pages, 5MB).
Parabola
Geometry
The shape of the quadratic function is called a parabola and obeys a very important rule. Say we have a sideways parabola: \[ x = f(y) = Ay^2. \]
Imagine rays (show pic!) of light coming from infinity from the right and striking the surface of the parabola. All the rays will be reflected towards the point $F=(\frac{p}{2},0)$ where $p = \frac{1}{2A}$.
( probably need a better drawing.)
Satellite dishes
You put the receiver in the focus point, and you get all the power incident on the dish concentrated right on your receiver.