This formula is not homogeneous, so something must be missing.
I suspect it is simply stating Total drag is the sum of induced drag + form drag.
For induced drag see:
https://en.wikipedia.org/wiki/Lift-induced_drag Since Lift = Weight (at 1g).
Induced drag is proportional to W^2/v^2
Form drag is proportional to v^2.
Hence Total drag is proportional to W^2/v^2 + v^2.