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Martin Sleziak
Martin Sleziak
11:33 AM
The question Finding the tenth derivative of $f(x) = e^x\sin x$ at $x=0$ was mentioned a few times on meta (mostly by Zacky). It seems to be in a process of delete/undelete war: math.stackexchange.com/posts/3077641/revisions
in CRUDE, Jan 28 at 21:18, by Martin Sleziak
A recent post on meta: Does this question deserve to remain deleted? The OP does not link to the question, but I guess it's the question 3077641 which has been discussed in this room.
Why would it be deleted? It's simple, those who do that just don't care about quality here on MSE. See another question math.stackexchange.com/questions/3077641/… that is highly appreciated, but it is deleted, here is how it looked: web.archive.org/web/20190119091049/https://… — Zacky 57 mins ago
0
A: Why would a question with an upvoted and accepted answer be deleted?

ZackyI would like to thank you for posting here and don't worry this isn't the only question that gets this treatment, as an example here would be another recent one with many great answers. In case of Page not found you can take a look at it here. It seems to me the rule you mentioned at the end of t...

There is a somewhat more general questions: $n$-derivative of function $f(x)=e^x \sin x$ at $x=0$. It contains at least some context - the OP calculated the first four derivatives. (From which it would not be difficult to go further.)
merging I suppose merging is not ideal, since some of the answers are specifically about 10-th derivative. But at least some of the answers generalize also to the n-th derivative. For example, Bernard's answer and Rhys Hughes' answer.
OTOH Bernard's answer is similar to Jacky Chong's answer. Rhys Hughes' answer is similar to Hans Hüttel's answer. Are there some other approaches on the deleted one, which are missing on the question which remained open?
I have at least added a bounty to the more general question:
2
Q: $n$-derivative of function $f(x)=e^x \sin x$ at $x=0$

Stepan VanzuriakI have function $f(x) = e^x \sin{x}$ and must found $f^{(n)}(0)$ $f'(x) = e^x(\sin{x} + \cos{x}) $ $f''(x) = 2 e^x \cos{x}$ $f'''(x) = 2 e^x (\cos{x} - \sin{x})$ $f''''(x) = -4 e^x \sin{x}$ $f'''''(x) = -4 e^x (\sin{x} + \cos{x})$ I think $f^{(n)}(0) = \alpha (-1)^n x^{2n+1}$ but I can't fi...

calculus derivatives taylor-expansion
On the deleted post there is also an answer by Taladris' which simply multiplies the two series. And an answer by David using Leibniz rule.
Probably making them into a form which answers the general question would need a bit of work.
it basically boils down to evaluating sum with binomial coefficients - I would expect a typical solution to use complex numbers in some way.
in TheSimpliFire's Chatroom, 31 secs ago, by Martin Sleziak
@Zacky You have deleted your question on meta: Does this question deserve to remain deleted? So it is no longer possible to comment there. I left a few comments regarding the question you discussed there in another chatroom.
 
Martin Sleziak
Martin Sleziak
12:17 PM
@Zacky I am not sure whether this does help much with the issue you're having with that question.
But at the very least I have tried to bring more attention to an already existing post on the site which is rather similar to the one you have mentioned on meta several times.
 
Zacky
Zacky
Thanks for this! Well personally I have nothing to win/lose from that question. I also agree that is similarly looking to many linked question by you, and maybe it should be closed for duplicate, or who knows?
But deleting it seems drastic and unreasonable.
All I can do for now is to rep-farm untill I hit 10k then proceed to contribute with one undelete vote.
That is boring anyway... Also I don't know how that process works, there can be delete/undelete war too?
 
Martin Sleziak
Martin Sleziak
But what is actually the site losing when this question is deleted - if almost identical question exists, with answers containing almost the same information?
Still, if you think it's reasonable to have apart from the question "What is n-th derivative of f(x)=exp(x)*sin(x) at zero?" to have a separate question "What is 10-th derivative of f(x)=exp(x)*sin(x) at zero?", a possible solution would be that you post that question yourself. (And keep in mind to include at least something which would qualify as context.)
You can then flag for merging - and if the moderators' consider this a reasonable request they can merge the questions. (I.e., move all answers from the deleted one to the new one.)
 
Zacky
Zacky
Almost identical, that is the point. I recall also a meta discussion where it explains why duplicates are useful, and well, that has 10 answers I think.
 
Martin Sleziak
Martin Sleziak
@Zacky Do you mean the fact that duplicates are useful for searching as mentioned for example in this answer: Avoiding duplicates?
 
Zacky
Zacky
12:34 PM
I don't think that was it, but quite similarly. Basically not only searching the same question using different terms, but also different terms in the explanation I believe is useful alot.
 
Martin Sleziak
Martin Sleziak
Yes. But the question was not closed and deleted because it is a duplicate.
 
Zacky
Zacky
Sometimes I tend to pick another similarly book when I study, just to see a duplicate explanation, but with different terms.
 
Martin Sleziak
Martin Sleziak
You have been around a bit. You've seen many discussions on meta explaining why low quality questions are bad for the site.
 
Zacky
Zacky
Well, I don't even know why it is deleted.
 
Martin Sleziak
Martin Sleziak
The entire question reads like this:
> I came across this Question where I have to find $$f^{(10)}$$ for the following function at $x = 0$
$$f(x) = e^x\sin x$$
> I tried differentiating a few times to get a pattern but didn’t get one, can someone provide the solution.
 
Zacky
Zacky
12:36 PM
That's why I asked the question on meta.
 
Martin Sleziak
Martin Sleziak
Well, you asked a question, but then deleted it - which means that people cannot answer your question now.
 
Zacky
Zacky
I tried differentiating a few times to get a pattern but didn’t get one. But he tried something.
 
Martin Sleziak
Martin Sleziak
So in your opinion this single line provides a sufficient context?
 
Zacky
Zacky
Of course it would have been better if he putted there explicitly what he didn't get.
No, but it's not zero context.
 
Martin Sleziak
Martin Sleziak
Personally, I am much more relaxed about including context than most of users around here. For example, if the OP included at least results they get when they (allegedly) differentiated a few times, I would consider the question to be perfectly fine.
 
Zacky
Zacky
12:40 PM
But as I saw from today's meta question: Before voting to delete, please check whether there are any good answers; if so, then the question should be flagged for moderator attention as a potential merge candidate. We don't like to lose great answers!
Doesn't this apply here?
 
Martin Sleziak
Martin Sleziak
I would not even vote to close as a duplicate - since it is possible that there are something which are more difficult if you want to calculate n-th term than 10-th term.
@Zacky Are you asking this seriously?
There is pleny of discussions on meta about this.
This previous discussion might be related: Deleting questions with answers. Some of the posts linked there might be of interest, too. — Martin Sleziak yesterday
Merely having an upvoted accepted answer seems rather irrelevant to the deleteability of a question. Maybe you should change to the actual content of your question “why was this question deleted with the off-topic reason?” Since you are apparently want to contend the applicability of the reason. — rschwieb yesterday
Although a lot has been said, I feel that it should be emphasized that the help center page referred to is network-wide, and does not allow for policy variations on individual sites. Therefore following standard SE reasoning it is less authoritative than site-specific meta discussions (like the linked threads). — Lord_Farin 13 hours ago
 
Zacky
Zacky
My point is that, the answer are useful and the question got a context included greater than zero.
Not enough maybe, but it's something
 
Martin Sleziak
Martin Sleziak
Well, let's agree to disagree. But certainly if other users see this as sufficient context, they will most likely vote to undelete. (To start the next round of deletion/undeletion.)
As far as I can tell, one more vote to undelete is missing before the whole things starts again.
 
Zacky
Zacky
As I said in the comments, I gave up with trying to argue in favour of it on meta. I only came here because you pinged me.
 
Martin Sleziak
Martin Sleziak
But can I at least ask whether you agree that without that one line the question would be worth closing and deleting? (I.e., just I came across this Question where I have to find $$f^{(10)}$$ for the following function at $x = 0$ $$f(x) = e^x\sin x$$)
 
Zacky
Zacky
12:45 PM
I believe the context is quite much
for example, this is actually zero context and it looks quite fine (up-voted, protected, not closed or deleted)
 
Martin Sleziak
Martin Sleziak
Yes. But it is an example from 2014. The site evolves.
 
Zacky
Zacky
Also I am sorry for bad english, maybe I said something and actually I meant something different.
As far as I can tell, one more vote to undelete is missing before the whole things starts again.
haha, I have to make 10k soon.
Anyway I think I sound ridiculous, so it's better to leave.
 
Martin Sleziak
Martin Sleziak
But certainly some people would argue that such old questions should be closed/deleted in such circumstances, too. This was discussed some time ago: Is it good practice to analyse past questions by today standards? Other questions linked there are related: math.meta.stackexchange.com/questions/linked/21773
 
Zacky
Zacky
How can a undelete war be ended?
 
Martin Sleziak
Martin Sleziak
I suppose by a moderator intervention. If a moderator deleted a post, it can no longer be undeleted by regular users.
The other option to end delete/undelete ware would be historical lock. (Somewhat related recent discussion: Historical lock for preserving old, low quality questions.)
 
Zacky
Zacky
12:51 PM
I see, then maybe one option should be taken.
 
Martin Sleziak
Martin Sleziak
And, of course, delete/undelete (or close/reopen) war can end simply if the users stop deleting/undeleting (closing/reopening) the question. But that is probably self-evident.
 
Zacky
Zacky
Yes, that is self-evident.
 
Martin Sleziak
Martin Sleziak
@Zacky Well, so far the question was closed and reopened once, it was deleted once and it has some undelete votes. I am pretty sure that if it goes through several delete/undelete cycles, moderators will take some action.
 
Zacky
Zacky
I see, thanks alot! I hope I didn't sound to ridiculous, it's hard to express a opinion in a different language than mine. Also I can be wrong with that question and I am just blinded now.
 
Martin Sleziak
Martin Sleziak
I should learn to type faster. Before I finish response to one your message, you usually already have posted another one. :-)
Thanks for taking your time to come here!
 
Zacky
Zacky
12:56 PM
No worries too! I appreciate alot that you got alot of tolerance. en.wikipedia.org/wiki/Toleration
 
 
1 hour later…
Martin Sleziak
Martin Sleziak
2:03 PM
@Zacky BTW the question was just undeleted. We'll see what happens next.
 
Martin Sleziak
Martin Sleziak
2:21 PM
> again this was only an example, it's hard to find many without enough reputation
Since you've mentioned searching for similar examples, I'll add that using SEDE you could be able to find similar post.
Still, below 10k you would not be able to see the actual question - just what was the score of the question, number of answers, scores of answers, etc.
I have mentioned some SEDE queries in my answer here: Are there some tools to follow deletions on this site?.
 
Martin Sleziak
Martin Sleziak
2:44 PM
67
Q: $100$-th derivative of the function $f(x)=e^{x}\cos(x)$

windircurseI've got this task I'm not able to solve. So i need to find the 100-th derivative of $$f(x)=e^{x}\cos(x)$$ where $x=\pi$. I've tried using Leibniz's formula but it got me nowhere, induction doesn't seem to help either, so if you could just give me a hint, I'd be very grateful. Many thanks!

calculus derivatives
HNQ is broken. Exhibit: The present question. — Did Jan 21 at 15:19
If you look at the questions mentioned above (and the one linked to them), this indeed shows that very similar questions (and very similar answer) can lead to rather different amount of reputation. (Although I think that this might sometimes happen even without the HNQ.)
 
Zacky
Zacky
3:27 PM
Oh, we will see. // That is indeed similar.
 

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