I plan to cite two sets of equations (referred to as Equations X and Y) from a paper. Equations X that hold for a model look like textbook results to me, but the authors give a lengthy explanation with a citation to another paper. Equations Y were derived for a special case of the model, since only the special case is useful in that paper. I am working on a different problem and will use this model. I need to include both Equations X and Y in my paper.
Is it appropriate to cite the Equations X followed by a similar but much shorter explanation as follows:
The following equations hold for these performance variables, as also seen in [citation]?
Is it enough or should more credits be given?
For equations X, it is quite obvious that it also holds for the general Model. Can I write something like the following?
[citation] has showed the above equation for the special case where L=0. It can be easily verified that it also holds for L>0.