I think the question was about the ½ wasn't it?
The equation is derived from the formula for kinetic energy, which is ½MV², from which the value for dynamic pressure: ½Rho.V² is reasonably simple.
If you look in pretty much any aerodynamics textbook (the grown up ones, not standard pilot training ones) you'll find the derivation of Bernoulli's formula, from which it's reasonably clear how this happens.
G