Is it really on topic to ask questions regarding an exact proof/how to approach the proof of a particular identity, or a physical equation?
3$\begingroup$ Two things: (1) physics is not math, so proofs are likely not on topic, and (2) questions on 'proving' equations found in undergraduate textbooks will likely be closed as too homework-like. $\endgroup$– Jon CusterMar 15, 2016 at 21:33
2$\begingroup$ Related: meta.physics.stackexchange.com/q/5713/2451 , meta.physics.stackexchange.com/q/5473/2451 , meta.physics.stackexchange.com/q/7140/2451 and links therein. $\endgroup$– Qmechanic ModMar 15, 2016 at 21:36
Simply asking "How does line X.Z come from line X.Y?" is likely to get your question closed as homework-like (or maybe unclear if you don't quote the relevant section of the text/paper you're referring to). So for it to remain open and answered, it needs to be framed to be about the physics of what the math is saying, rather than how to do the math.1
For example, one could ask about the assumptions underlying the derivation, but I think it important to include your expectation of why you think something is screwy with the derivation (e.g., Why do we take the small x limit here, can't x be big because Reason Y?).
1. Such a question would likely be on topic over at Math.SE.
2$\begingroup$ I'm kinda curious what there is to disagree with here. $\endgroup$ Mar 18, 2016 at 15:56
1$\begingroup$ Is it the first or the second paragraph that's caused the downvoters to vote as they did? Because, AFAICT, this is what actually occurs presently. I'm fine with the disagreement, but would like some clarification (which would only go to help the discourse). $\endgroup$ Mar 19, 2016 at 16:31