Puntosaurus, don't forget the wing or rotor is only required to generate enough lift to lift the aircraft. For a bounded wing in free air it would need to be infinately long, so each segment would be required to produce zero lift. So for a practical wing it is fair to comment about the induced drag being a function of the vortex strength. As for the equation being unfathomable - that first link put up by Nick is well worth a peruse for some of the equations.