A request for input: how should one handle a question like this one? If the proof is wrong, then a good answer is an explanation of why the proof is wrong. On the other hand, if the argument is correct, a "good" answer is "Yup."
Are these kinds of questions at all useful? I kind of feel like they aren't...
@XanderHenderson For what it's worth, the site explicitly allows proof-verification questions.
I am personally fine with it, though it frequently is in conflict with the stated SE goal of becoming a repository of useful information. However, there are a few cases where the proof-verification question is actually worth keeping for future students who may come across it. In any case, I am fine with any question that arises from an honest inquiry with effort shown, regardless of whether the answer could be just a single "yup".
@Did @amWhy @XanderHenderson: As always, there are some nonsense answers to questions about sqrt: here and here. The latter's first equation is nonsense.
@JohnMa I decided to delete (2) because the accepted answer treats "y = x^2 for x≥0" as a function, and also does not state precisely the domain, making it quite misleading to future clueless readers.
The question itself is not so bad, but the asker chose a bad answer (that didn't even point out clearly that sqrt is defined in a certain manner, not just in some so-called algebraic view). Furthermore, the algebraic view is actually to not require the square root to be a particular choice...
@DanielFischer: Hello! It's been a while since I saw you here.
Underwood Dudley published a book called mathematical cranks that talks about faux proofs throughout history. While it seems to be mostly for entertainment than anything else, I feel it has become more relevant in modern mathematics. Especially with the advent of arXiv, you can obtain research pa...
