For anyone interested in why there's a lot more to it than this argument, the first equation: Mg = C1 * Rg * Rg Is not a good assumption for the discs we obse

For anyone interested in why there's a lot more to it than this argument, the first equation: Mg = C1 * Rg * Rg Is not a good assumption for the discs we observe in the universe, because they do not have a constant surface density. The picture is further complicated by the fact the many disc galaxies also contain a central bulge, large enough to effect the potential (to say nothing of Dark Matter).