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2790867, 3285344, 3285270. 1829808 were undeleted.

room topic changed to GENTLE: This chatroom is trying to save useful content from MSE. Most of which is erased by CRUDE users. Anyone is welcome here to post links to wrongfully closed/deleted questions. (no tags)

room topic changed to GENTLE: This chatroom is trying to save useful content from MSE. Most of which is erased by CRUDE users. Anyone is welcome here to post links to wrongfully closed/deleted questions that needs correction. (no tags)

room topic changed to GENTLE: This chatroom is trying to save useful content from MSE, most of which is erased by CRUDE users. Anyone is welcome here to post links to wrongfully closed/deleted questions that needs correction. (no tags)

One more undelete vote would be apreciated here: math.stackexchange.com/questions/2493482/…

Man, I'm bad at this.

I don't know how to post in Martin's format.

I wouldn't really call it Martin's format, it is simply MarkDown.

[How does one evaluate $1+2-3-4+5+6-7-8+\cdots+50$?](https://math.stackexchange.com/q/2493482) yields How does one evaluate $1+2-3-4+5+6-7-8+\cdots+50$?.

I use a bookmarklet to get link of such form faster.

From here: web.archive.org/web/20180401234620/https://…

The one I use for this is "Formatted link to a webpage."

When I get to Math.SE question/answer, after clicking the bookmarklet I get [text](url) where url is the link to the question (answer) and text is the title of the question or the text which is currently select.

The only problem is that this messes up the title if there is MathJax - in such cases I need to do a few more clicks - I click on edit and select the title. (Then the bookmarklet uses the selected text.)

I use it in Google Chrome, I haven't had any problems with it.

An undelete here is appreciated: Integral $\int_{0}^{2\pi} \ln (2\sin(\frac{x}{2}))dx$

It works! Thank you.

Well, thanks mainly goes to the user who created the bookmarklet(s). (That goes far beyond my programming abilities.)

Sorry for the off-topic messages - it seems that so far there are more messages here about how chat works than the intended purpose of the room.

Two more undelete votes needed here: Partial-fraction-without-defraction

@MartinSleziak And the "R" stands for "Reopen."

@Zacky The intention of CRUDE was to create a public and transparent forum for discussing problematic posts (either low quality posts which should be closed or deleted; salvageable posts which require some editing or other extra attention; and posts which should be either reopened or undeleted (either because they shouldn't have been closed or deleted in the first place, or because they have been improved and should now be reopened or undeleted).

By refusing to engage in CRUDE, you isolate yourself from that discussion, and your voice isn't heard.

While we obviously disagree about what constitutes a "good" answer which is of high enough quality to preserve an otherwise poor question, we likely agree about many other things. It would be unfortunate to lose your voice from the process.

You are of course welcome to come here and help saving good content, but please keep the room on-topic.

This question needs one more undelete vote: Partial-fraction-without-defraction-for-an-integral

@Zacky Can you explain why you want to preserve that question? The question itself is quite clearly not in line with site standards, and the only answers are a "hint" which does not completely answer the question (I'll note that there are differing opinions on hint answers), and your answer which does not use the approach requested by the asker, and instead depends on a non-obvious substitution.

Yes, OP could've brought more background, but it's not inexistent. It's understandable from what he mentioned that he got an integral out of thin air and by pure curiosity wants to see an easy way to solve it.// I agree that to get that substitution from scratch will be rather hard and unobvious.

But hey, partial fractions where unobvious for me too when I first learnt about them. And who even said that something must be obvious? I also think that the substitution is rather unknown, if one deals alot with tricky integrals then he will notice easily when such a substitution is obvious.

If you look in the comments you will see that many users aren't even aware that it's possible to avoid partial fraction and get something easy as OP wanted. Also I think my answer really helped some users.

@XanderHenderson "...and your answer which does not use the approach requested by the asker, and instead depends on a non-obvious substitution." about this, this doesn't count as a point/motivation to delete a question. In my experience, sometimes I have asked for x and instead users reply with y ;and it turns out it works aswell, you learn a different approach, different point of view, etc. So it benefits you.

@Zacky Are you arguing that the question is within site standards? As I read the question, all it states is (1) here is an integral (2) which I am supposed to evaluate using partial fractions (3) but partial fractions are hard. One can infer that the student is a beginning calculus student, but this isn't made explicit. That is context which would be helpful to have.

At the very least, some description of what they know of partial fraction decomposition would be helpful to know.

@Isa I would argue that a poor question should be deleted unless it has attracted a great answer. Zacky's answer doesn't actually answer the question asked (in that it introduces a non-obvious substution without justifying that substitution), and is otherwise a fairly standard computation. Personally, I would rate that answer somewhere between "okay, but not good" and "slightly good". Certainly not "great".

Do you believe that Zacky's answer is "great"?

@XanderHenderson idk I can't see it. I was referring to the general case.

When you ask for something but instead got something else

@Isa In the case of the question being asked, I infer that the asker is a beginning calculus student who has just been introduced to the concept of partial fraction decomposition for evaluating integrals. They were given a rational function to integrate where the denominator is of the form $x^3 + a^3$, and asked to find a partial fractions decomposition. Since the goal of the exercise is to practice a particular technique, using another technique doesn't seem like a useful answer to me.

That being said, it is possible that my inference about the goal of the question is incorrect---this is a problem that could be solved by the asker, if they chose to provide more context.

Are you arguing that the question is within site standards? He brought some background: This is part of the training to solve other kind of integrals where it's not so easy to find a partial fraction.

So the answer to my question is "Yes, I [Zacky] believe that the question is within site standards."

If that is the case, then we disagree, and I am not going to try to convince you otherwise.

If (as you seem to believe) the question is within site standards, then the quality or relevance of your answer is moot.

Btw, I also posted my solution only after an answer that shows a way with partial fraction was posted.

I would rate that answer somewhere between "okay, but not good" and "slightly good". Certainly not "great". Thanks, for the feedback I guess!

There is no answer which shows a way with partial fractions. There is a hint "answer" which shows the general form of a partial fraction decomposition. That "answer" is, at best, a comment. But, as I said, the quality of your answer is irrelevant if you believe that the question is a good question.

I already said that OP could've brought more background, but it's not inexistent.

As to my opinion of the quality of your answer, I have already explained my reasons (and given more complete feedback than "it is only okay"). My main beef is that you use a non-obvious substitution, and the best explanation that you can find for that substitution is "trial and error".

It's not a question that deserves to be closed therefore.

@Zacky So, we disagree---I agree that there is some background, but I do not believe that there is sufficient background or context. But, again, I doubt that either of us is going to convince the other.

Wait. I mentioned that I found it from scratch with trial and error! I also found partial fraction through the same approach (that I'm quite proud of) only to realise afterwards that it's widely know. All math is through trial and error for me untill I learn somehting.

No one needs to be a Ramanujan and do everything perfectly from the first try.

Now that I got comfortable with a few integrals, I can easily see when to use which substitution. And still I find more for myself from trial and error, I'm sorry if I don't do things your way.

"I also found partial fraction". A different way that I learnt in high school I should rather say.

(1) the sum / difference of cubes formula is part of the standard precalc curriculum in the US (and, I assume, in the rest of the world)---students should know that formula; (2) even if one does not know the sum of cubes formula, it is not hard to note that $-a^{1/3}$ is a root of $x^3 + a^3$; then polynomial division gives a factorization---there is no need for trial and error.

I don't understand what you're refering to now. Also why do you need x^3+a^3? One needs only the formula for x^3+1 there.

In any event, I (and this is my opinion, to be clear) feel that any answer which relies on a clever non-obvious substitution, or a magic value of $\varepsilon$, or on any other similar trick is not a good pedagogical answer. Some might consider such solutions to be "elegant", but I think that students and learners are much better off seeing an elementary approach where each step can be justified and motivated.

@Zacky What don't you understand?

@Zacky This explains what the substitution does. It does not motivate the substitution at all, nor does it explain any kind of general technique by which one could come up with such a substitution.

What is the usage of (1) ? I answered (2).

Haha, I need to go back in time and tell that to my teachers.

The sum and difference of cubes formulae are part of the introductory curriculum in the US. That is, any student who is taking calculus in the US is supposed to have learned in a previous class that $$ x^3 \pm a^3 = (x\pm a)(x^2 \mp ax + a^2). $$ This previously memorized formula allows one to factor the denominator $n^3 + 5$ in the given integral.

Ah, now I see. You Ignored the part when I subbed n=\sqrt[3]{5} x. Afterwards we only need x^3+1.

But, as I said, if one has not memorized this formula, then it is simple enough to note that $-\sqrt[3]{5}$ is a root of $n^3 + 5$, and so $n+\sqrt[3]{5}$ is a factor of the denominator. Then polynomial division finishes the problem.

@Zacky I didn't ignore that part of your answer; I ignored your answer entirely. I have been referring to the question itself in discussing the partial fraction decomposition.

Oh. You shouldn't ignore that. It's an useful substitution :)

I disagree, but that is a matter of opinion.

Sure then, I can respect your opinion.

Anyway what is the point of this conversation?

Well, part of your argument about undeleting a particular question was that you had provided an excellent answer. I disagreed with your assessment of the quality of your answer, and was trying to explain that disagreement.

I see, thanks! I also disagree with your disagreement.

with your explanation for the disagreement*

@Zacky Obviously. It is a matter of opinion. I do wonder, however, how many times you have taught integral calculus, and how much experience you have with the reaction you get from students when you pull a magic substitution out of nowhere. ;)

You got me here, haha..

Although it doesn't matter, I'm in college and I don't do anything related to math there. I'm obviously not a teacher.

But for some unknown reason I do math in my free time. I often try to stop, but it's really addicting.

@Zacky The point was not meant as a criticism. Your answer is not wrong; it simply isn't very pedagogically useful (in my opinion). As I see it, a good or great answer on MSE should be illuminating to the asker---it should help the asker to understand something about the problem that is being asked.

As I read it, the goal of the partial fractions question is not to evaluate the integral (because, let's be honest, a computer algebra system can do it faster and better than I can), but to practice using the technique of partial fraction decomposition.

An answer which does not use partial fraction decomposition is already slightly off-topic, an if that answer uses a sneaky and unmotivated substitution, it goes even farther afield. I (again, my opinion) don't think that such an answer is terribly useful to the person asking the question (though I imagine that they might be satisfied with such an answer, because they might mistakenly believe that the goal is to evaluate the integral, rather than to practice a different skill).

It seems like you imply that only teacher should post answers around here. I tried my best to explain there and OP liked that, why do you say otherwise?

Again, OP was fine with having a different and easier solution.

I'm talking about the comments that me and OP had in my answer.

I doubt that a computer can come up with such a substitution anyway.

After all they are simply brute forces, like any answer with partial fractions.

@Zacky I did not imply that. What I suggested is that because your answer focussed on the result, rather than the process, it seemed clear to me that you had not taught in the past. This is neither positive nor negative. Rather, I am trying to share with you what my experience has been teaching such classes.

And I am not claiming that a computer will come up with a better substitution. I am suggesting that if the goal were actually to evaluate the integral, then it would be faster to fire up Maple or Mathematical or whatever, and just have the computer evaluate the integral.

Do you really make everything obvious when you teach?

That seems impossible to me. Also every teacher I had was just trying to get students pass an exam. In the end what's the goal?

@Zacky What do you mean by "Do you really make everything obvious when you teach?"

I don't understand the question...

I had this in my mind: As I see it, a good or great answer on MSE should be illuminating to the asker---it should help the asker to understand something about the problem that is being asked.

Yes, and?

I took this for teaching (in real life too).

Which wasn't related, I guess I'm getting tired. Sorry!

Yes. I think that good instruction should be illuminating. And?

One more undelete vote needed here

done

though i'd say the answer is a bit too much on the hint side to make this high prio

also it doesn't really answer the question

to answer it fully, it would have to show that no other number can be removed instead

but i like the question :) used it in my class already

ok, will jagy doesn't prove uniqueness either

Well, I also see that OP brought the source and previously edited he mentioned that he has absolutely no idea. This is clearly non-missing context.

@Zacky All sources were later added by Jack

Yes, that's true.

But that's a good thing.

oh right, bertrand's postulate yields the uniqueness. feels like overkill though

Sorry, I had to google Betrand postulate to see what that is :(

@TheSimpliFire I just realised that I wrote "I also see that OP brought the source", sorry! Jack was the one who made the question decent.

actually i was wrong: it's Erdos-Selfridge, not Bertrand :)

IMO this kind of things is useful, but in the same time, maybe the question should be made community wiki.

I remember that recently @XanderHenderson did the same thing to a question (made it nice bringing context), unfortunately I don't recall if that was made cw and I can't find it now.

Thanks! My comments were deleted apparently, that's why I couldn't find the question..

answered hopefully for good

@Zacky but it's really not the same thing. Plus it was apparently a duplicate. So if anything, it should have been closed right away as such.

Basically it was all just a giant waste of everyone's time.

Well, at least in the end some good came of it. Maybe let's say the glass is half full.

That looks fair.// Also since we're at it, isn't it a good idea to make that linked question from above community wiki? Or I mean in general, if someone takes the question in his own hands to make it nice because the OP doesn't care (or is missing), then OP shouldn't benefit from that. (I thought about asking on meta this idea, but maybe it isn't necessary).

@Zacky generally we do not want a proliferation of CW (here "we" is also SE generally). If everybody just would not answer poor questions there would be no problem. I really do not see why we should jump through all kinds of hoops to navigate this situation.

@Zacky I flagged the question and asked if it should be made CW. The moderator response was "For the most part SE wants to get rid of CW questions. There is not ideal way to go about this. If you want, you can create a meta post, but really just if you want."

The post in question is about the power rule

Oh... @TheSimpliFire found it first. I should read to the end before commenting.