# Why was my question about the Devil's problem deemed a homework question?

My recent question was manually removed from Hot Network Questions and later closed as a homework question, but it eludes me why.

According to the FAQ on homework questions, the definition of homework question is:

A "homework question" is any question whose value lies in helping you understand the method by which the question can be solved, rather than getting the answer itself.

The purpose of my question was, on the contrary, to ask whether 13 is really the answer for the problem described in my post. The very title of my question is: Is 13 really the answer for the Devil's problem in physics? As I explicitly wrote in my question, I don't study physics. I liked physics at school, but I'm now a university student studying languages, as you can see from my posts on other SE sites. My motivation, as explicitly stated in my question, was this: It's mystical and a bit scary if the Devil's dozen really pops out of nowhere in such a simply stated problem.

I wasn't interested in learning or understanding any physics methods; my interest was to find out whether 13 is indeed the answer for the problem in question. It's the Devil's dozen that made me interested. For me, the value of the posted solutions is that they prove that 13 is indeed the answer, not that they teach me a method.

I did imply in my question that I wanted to see a solution, but that was merely because I wanted to verify. I wanted to get convinced whether 13 is the answer. And I thought that people reading my question would want to get convinced, too.

Since the posted solutions confirm that 13 is the answer, I don't really need any more answers there, but if the question remains closed, visitors won't see it and thus won't be able to appreciate the beauty of the problem and its mystical appeal.

My question was well received by SE users, getting 25 upvotes and becoming followed by 12 users.

Is my question really a homework question, and if so, why?

UPDATE: An answer below suggests that my question is rather a check-my-work question. However, my question doesn't fit the definition of check-my-work question:

It's long overdue that I make this post revisiting our policy on "check-my-work" questions. These are questions, often (but not necessarily) homework-like, that present a complete mathematical or logical derivation and ask whether it's correct.

The word "complete" is made italic in the original definition, so it's not my emphasis. My question doesn't present any derivation at all. It merely presents a problem and asks whether its answer is 13. I asked to solve the problem. How can it be a check-my-work question?

At any rate, shouldn't the rules be interpreted in view of their actual intent as well as the mission of the Physics SE? My impression is that the rules about homework and check-my-work questions are there to protect the Physics SE from boring, low-quality posts by lazy students. My question is very different. I believe I posted a very interesting high-quality problem that is especially appealing in view of its elegant and mystical answer. Such problems belong to the physics folklore, and the reaction of the community to my question speaks for itself.

Please ask yourself a simple question: Does the post about the Devil's problem make the Physics SE a better place? I'm relatively new to the Physics SE and will trust your judgement, but I do want you to ask yourself that question. If you judge that it is to advantage of the Physics SE to hide my question from visitors, so be it.

UPDATE 2: My question got re-opened and later re-closed. I appreciate the detailed answers below, but, to be frank, I cannot but shrug my shoulders, especially when reading arguments like "just being interesting does not make something on-topic." Sure, an interesting question about biology isn't on-topic on Physics SE, but why wouldn't an interesting question about physics be on-topic there? My question is about physics and is interesting, as evidended by its popularity. I agree that most homework-like questions should be considered off-topic, but only because they are boring and uninteresting. To put it simply, homework-like is a code word for uninteresting.

Furthermore, if my question about the Devil's problem deserves to be closed, why doesn't my question about a magic wall deserve the same? It's a classical homework problem, and moreover, I posted that question because a friend of mine, who studies physics, got that problem for homework. He mentioned the problem in a casual conversation with me, and this is how I got interested, which eventually led to me posting that question. So why didn't anyone vote to close it? I am perplexed by such inconsistency of your moderation. As a side remark, it's disappointing that no one on the Physics SE was able to post a valid answer for that homework problem, as my friend later learned from his university lecturer.

Now, for the sake of demonstration, I've just posted an intentionally boring, uninteresting question. I'm pretty sure that because of your flawed policies and practices, it will be deemed on-topic and remain open, whilst my popular question about a fascinating mechanics problem will remain closed.

• FWIW, I am one of the close voters, and I did upvote your question at the time I voted to close it. I upvoted your question because it's a good question (kudos!). But I voted to close because such questions aren't suitable for Physics SE according to the current policies. So upvotes and favorites shouldn't be a good metric to judge the on-topicness of your questions. However, here, most of the positive exposure this question got is because of a click-baity title, an interesting (homework-like) problem and the HNQ. – user258881 Jun 28 '20 at 15:27
• @FakeMod : If it were just a click-baity title, why would many people upvote the question and make it favorite? If the popularity of my question is merely due to the HNQ, how would my question become a HNQ, in the first place? And if the problem is really interesting, isnt it a good reason not to close the question? – Mitsuko Jun 28 '20 at 16:38
• @Mitsuko the number of upvotes is irrelevant here. Sorry but you did no work towards the solution, could not identify any conceptual difficulty with this problem, and did ask for a solution. As a result your question as phrased is regrettably not suitable for the site. – ZeroTheHero Jun 28 '20 at 16:41
• Even this was an interesting problem, however, interesting-ness and off-topicness are mutually exclusive. I, more or less, agree with your first two counter-arguments, but not the last one. – user258881 Jun 28 '20 at 16:42
• @ZeroTheHero : >> Sorry but you did no work towards the solution << I disagree. Please kindly have a look: physics.stackexchange.com/a/562237/253093 – Mitsuko Jun 28 '20 at 16:43
• For what it's worth, the question is currently reopened, though I disagree with that for reasons stated in my answer. – JMac Jun 28 '20 at 16:44
• @FakeMod Those are contradictory indicators. An up vote means you think the question belongs on the site. A close vote means you think it doesn't belong – BioPhysicist Jun 28 '20 at 16:45
• Well if you want to include elements of your answer as part of your question I encourage you to do so as an edit, and indeed encourage you do,to so when you originally post the question. – ZeroTheHero Jun 28 '20 at 16:47
• There is no limit on the length of a question. – ZeroTheHero Jun 28 '20 at 16:53
• I think the title is appalling clickbait and completely support the removal from HNQ. I find the idea that there is anything mystical and scary about the number 13 to be offensive on a site about physics. I did not vote to close the first time, but I have voted to reclose. I definitely consider it a homework-like problem. – G. Smith Jun 28 '20 at 20:50
• The answers should be deleted and replaced with a one-word answer, “Yes.”, because this is all the OP claims to have wanted to know. And then this can remain an interesting problem for students to work out for themselves without copying their answer from this site. – G. Smith Jun 28 '20 at 21:06
• @Mitsuko The fact that your title was clickbait is why it got so many upvotes from users outside of PSE from the HNQ. – BioPhysicist Jun 30 '20 at 18:01
• It is an automated system. I am not entirely sure how it works. But what I can say is that it greatly inflates the number of votes and views from people who are not familiar with PSE. You can't point to your votes on this question then to say how good the question is. The HNQ tampered with the voting essentially. Most people on PSE hate the HNQ since it typically features questions that do not reflect what PSE. I am just trying to help you, I suppose. Your argument about the number of votes makes the argument less credible due to the fact that your question made it to the HNQ list. – BioPhysicist Jun 30 '20 at 19:49
• @Mitsuko If it had been just clickbait, people wouldn't have upvoted my question that many times. That is exactly what clickbait aims for and often accomplishes, on this site and elsewhere. I am not going to take part in the discussion any further. I think that the sentiment on your position is quite clearly against it. – G. Smith Jun 30 '20 at 19:55
• The most important thing for becoming HNQ tends to be the number of answers and the scores on those answers, not the upvotes on the question. As documented here and here. – Chris Jul 1 '20 at 0:21

Your question does not ask a conceptual question about physics, it simply asks users to solve the exercise you call "the Devil's problem".

That you ask us to solve the exercise not by saying "Solve this for me" but by asking whether a given number is the answer doesn't change anything in my eyes - how is an answer supposed to make the argument that this is or is not the correct solution without actually solving the exercise?

Our policy about on exercises and homework questions isn't about playing word games, with this argument you could make any "Solve this" question on-topic by claiming an answer and asking if it is true. Note that this maneuver is frequent enough that we have a dedicated meta post about check-my-work questions which is also linked in the closing notice. That your question doesn't contain any work except a claim of what the answer is doesn't exactly improve the argument for its reopening in my eyes.

You seem to be taking an extremely literal approach to the formulation you quote. The phrase

A "homework question" is any question whose value lies in helping you understand the method by which the question can be solved, rather than getting the answer itself.

does not mean that just because you don't care about the method by which one arrives at the answer it is automatically on-topic. This interpretation would make any homework question on-topic if and only if the asker really doesn't care about learning anything and just wants to hand in the correct solution, which is clearly not the intention.

It is instead meant to describe the typical intention of someone giving this exercise to someone or someone finding this exercise in a textbook (ideally students do not do exercises to get marks but in order to apply and train what they have learned). The specific intent of an asker is irrelevant - we judge questions by their content, not by whatever is going on the mind of the person who asks them.

• >> does not exactly endear me to claims that this question's exceptional popularity is due to some "mystical appeal" rather than simple clickbait mechanisms << If it were just a click-baity title, why would many users upvote my question and make it favorite? – Mitsuko Jun 28 '20 at 16:17
• I don't think it's clickbait. I literally teach Newtonian mechanics for a living and have seen thousands of problems, and this one was novel and interesting to me. – knzhou Jun 28 '20 at 16:39
• Whether or not the question is "clickbait" wasn't relevant to anything in the rest of my answer, so I've removed that passage to avoid tempting users to discuss that instead of whether or not the question should be closed. – ACuriousMind Jun 28 '20 at 16:44
• >> Your question does not ask a conceptual question about physics, it simply asks users to solve the exercise you call "the Devil's problem" << Let's open the most popular question on the Physics SE. The question reads: What is the fastest method to cool a cup of coffee, if your only available instrument is a spoon? Like me, the OP didn't ask a conceptual question about physics. Like me, he or she wanted people to apply physics laws of their choosing and come up with a solution. – Mitsuko Jun 28 '20 at 18:53
• The OP wanted a qualitative solution, whilst I wanted a quantitative one, but I don't think it makes a principal difference. Fundamentally, many questions on the Physics SE are solve-this-for-me questions. – Mitsuko Jun 28 '20 at 18:55
• I think the real criterion is, or at least should be, whether a post is about a boring textbook-like problem of interest to few users of this website, or, on the contrary, about something quite interesting. And many users found my question interesting. – Mitsuko Jun 28 '20 at 19:03
• @Mitsuko While everything that is on-topic should be interesting to someone, just being interesting does not make something on-topic. Neither does being popular. – ACuriousMind Jun 28 '20 at 19:11
• Sure, an interesting question about biology isn't on-topic on Physics SE, but why wouldn't an interesting question about physics be on-topic there? My question is about physics and is interesting, as evidended by its popularity. I agree that most homework-like questions should be considered off-topic, but only because they are boring and uninteresting. To put it simply, homework-like is a code word for uninteresting. – Mitsuko Jun 30 '20 at 17:42
• @Mitsuko The "popularity" is invalid because your question made HNQ. I think your problem is very interesting. But the way you posted it, what you chose to focus on, etc. made it not ideal for PSE. However, no one is saying the question is poor in general. It is an interesting question. – BioPhysicist Jun 30 '20 at 17:59

First, note that not all homework related questions are off topic here. However...

I wasn't interested in learning or understanding any physics methods; my interest was to find out whether 13 is indeed the answer for the problem in question. It's the Devil's dozen that made me interested. For me, the value of the posted solutions is that they prove that 13 is indeed the answer, not that they teach me a method.

This is actually precisely what makes your question off topic IMO. Homework questions that are on topic here are ones that do ask about physics concepts and methods and don't ask just for solutions/proofs. This is explained in the FAQ you linked to. I suggest reading it further.

My question was well received by SE users, getting 25 up votes and becoming followed by 12 users.

Your question made it to the Hot Network Questions list through an automated process. As such it was probably viewed by many users who are not familiar with PSE policies. The votes therefore are not a good indicator of the question's quality in this case.

• >> Homework questions that are on topic here are ones that do ask about physics concepts and methods and don't ask just for solutions/proofs << What makes you think my question is a homework question, in the first place? The definition in the FAQ is: A "homework question" is any question whose value lies in helping you understand the method by which the question can be solved, rather than getting the answer itself. I wanted to get the answer itself. So how is my question a homework question? – Mitsuko Jun 28 '20 at 14:39
• @Mitsuko Your question is "homework-like". No one is saying your question is assigned as actual homework. You are asking for a solution to a physics exercise. To me that is "homework-like". – BioPhysicist Jun 28 '20 at 14:53
• Aren't a homework question and a homework-like question equivalent terms for the purposes of closing questions on Physics SE? My impression is that these two terms are used interchangeably and mean the same on this SE. After all, the definition of a homework question doesn't say that a homework question is actual homework. – Mitsuko Jun 28 '20 at 15:02
• @Mitsuko We don't close all homework-like questions. But we do (try to) close those that focus on just getting or verifying a particular numerical answer. So by saying "I wanted to get the answer itself" you are giving us evidence that your question is, in fact, off-topic. FWIW, I didn't downvote or close-vote your question because it looked like it was attracting interesting answers. OTOH, at this stage, I don't feel that I should vote to reopen it. – PM 2Ring Jun 28 '20 at 15:57
• @Mitsuko The entire reason we use the term "homework-like" is to represent that it is not quite the same thing as being an actual homework problem. – David Z Jun 28 '20 at 22:02

I did imply in my question that I wanted to see a solution, but that was merely because I wanted to verify. I wanted to get convinced whether 13 is the answer.

We call these check-my-work questions. Yours is exceptionally interesting, and perhaps the community will vote to reopen it on that merit. But generally check-my-work questions are not high-quality, so we have a guideline which suppresses them.

• "Yours is exceptionally interesting, and perhaps the community will vote to reopen it on that merit.": Then I suppose the community's decisions are flawed if it does this, right? I mean, deciding the off-topicness of a homework-like or a check-my-work question by it's difficulty or beauty doesn't seem the right way to go, IMO. It would be nice if you would also agree, and thus kindly remove such a statement from your part. – user258881 Jun 28 '20 at 15:16
• Thanks, I've just added an update to address this. – Mitsuko Jun 28 '20 at 16:35
• @FakeMod There are some people who might argue that these types of questions should be allowed. I think it's fair to say they have a right to cast a reopen vote if they feel the question is a good fit. If it were reopened though, it could still also be closed again. If that were to happen, I doubt it would get enough reopen votes a second time, though a second closure might also be a bit of stretch. – JMac Jun 28 '20 at 16:37
• @FakeMod, I have a public affection for interesting questions. I view the guidance about on- and off-topic questions as an attempt to describe what the community wants, rather than a contract to which we are bound. Sometimes we get a great question that superficially breaks one of our rules; I am loath to discard such content because of a rule meant to prevent something else. If we find ourselves making many such exceptions, we can have a Meta discussion about whether to write different guidance. People change over time, after all. – rob Jun 28 '20 at 18:47
• @rob Thanks for explaining! I see your point :-) – user258881 Jun 28 '20 at 19:11
• @FakeMod “interestingness” is subjective. I also find it interesting but it does not belong to the site. I mean: I’m sure for every question there will be some who find it interesting. Find me an OP that willing posts a boring question? – ZeroTheHero Jun 28 '20 at 19:50
• @ZeroTheHero My personal take on that is that there's some onus on the person asking the question to point out why it is interesting from a physics perspective, which to me, generally requires more than just posting a question that ends up having an interesting solution. – JMac Jun 28 '20 at 20:17
• @ZeroTheHero Of course it's subjective. We're here because we are people who enjoy asking and answering questions about physics, and all enjoyment is subjective. As for people who intentionally post questions they find boring, I would say that's exactly what the homework policy is meant to squash: boring questions about inclined planes from people who don't care about them. My opinion is that interesting questions which happen to turn into a calculation are often collateral damage from our strictly-interpreted homework policy. I think we could benefit from being more judicious in what we keep. – rob Jun 28 '20 at 20:19
• @rob Right. It seems then that homework-like is code word for “uninteresting”... Look: we can try splitting hairs but this question - which I find interesting - could have remained closed and nothing would have been lost. There is already an accepted solution. Deleting? No. Closing: IMO yes, and I say yes because I would not want to encourage this generic type of question. Will some HW make it through and not get closed? Sure. No big deal. – ZeroTheHero Jun 28 '20 at 20:33
• @ZeroTheHero Probably, you misunderstood my first comment. I am also of the opinion that "Interesting-ness" should not factor in during the closure of a question :-) – user258881 Jun 29 '20 at 11:11

With due respect, I think you're missing the larger point here. This question may or may not be a homework-style question to you, but it is definitely a homework-style question for the site. In other words, what matters is the value of the question to the site rather than to the OP.

Don't get me wrong: this is a cute problem. I'm likely to use it as an example in my class (including the excellent elements of solutions) but I cannot use it as an assignment problem precisely because students in my class are smart enough to just look up the answer on this site.

If you were just looking for someone to confirm that the answer to the problem was 13 without showing any work, I don't see how that would make the question a better fit for the site.

To me, that would be off topic as a "check my work" type question, and a particularly bad one because no work was shown. An answer of "yes" would not be useful to future readers without a derivation of why.

This site is better suited to conceptual questions which can be useful to future readers as well. If, for example, you had been looking at a solution to this problem and were trying to understand how/why a specific concept was applied, that is more likely to be on-topic.

The word "complete" is made italic in the original definition, so it's not my emphasis. My question doesn't present any derivation at all. It merely presents a problem and asks whether its answer is 13. I asked to solve the problem. How can it be a check-my-work question?

If you're just asking to confirm the answer is 13, then it's clearly a very poor fit for this site. That meta question you linked does seem to single out check-my-work for complete answers; because that is a more nuanced subject. Asking, "Is the answer 13, and how would you get that answer?" seems off topic for being a check my work and being a homework and exercise question to me.

It merely presents a problem and asks whether its answer is 13. I asked to solve the problem. How can it be a check-my-work question?

You asked if the answer was 13, so you're asking to check "the work" (that isn't presented), and then for a solution, which seems to definitely fall against the homework and exercise policy.

At any rate, shouldn't the rules be interpreted in view of their actual intent as well as the mission of the Physics SE? My impression is that the rules about homework and check-my-work questions are there to protect the Physics SE from boring, low-quality posts by lazy students. My question is very different.

It doesn't really seem that different to me. You presented a question and then offered no attempt to solve it. For all we know, you were assigned this question, and knew the answer was 13, and decided to frame it as "the devil's problem" to get an answer as a "lazy student".

We treat the questions based on the content, and your question doesn't actually provide any conceptual physics question. It's purely a physics exercised framed with the story of how you came across it. You're just telling a story of how you doubt that answer, and want to see the solution. When you distill out the details, it's a basic homework and exercise question, or check my work.

Please ask yourself a simple question: Does the post about the Devil's problem make the Physics SE a better place?

In my opinion, no. We have these policies because the active community here decided we don't want to be answering exercise questions for others. We are willing to address conceptual problems that may arise when solving it, but you never attempted that. The fact that some people thought it was good (many probably not particularly active here because it was a hot network question so people across the network can upvote it), doesn't mean it's a good fit for this site. Having it open and in hot network questions could serve as an example to others that such questions are acceptable, which is against the current policies on the site, and could actually cause harm here in my opinion.

• No, I did imply in my question that I wanted to see a solution. I explicitly wrote, "How can this problem be solved?" I wanted to verify that the answer is 13. And I even found a mistake in one of the proposed solutions, as you see in my comments there: physics.stackexchange.com/a/562108/253093 So I was interested to see a solution, but not for learning a method. – Mitsuko Jun 28 '20 at 14:30
• @Mitsuko The "intent" in our policy is not about what you, personally want to learn when you ask a question, and you're focusing too much on what you think the literal meaning of that small part of the HW policy is. Trying to argue that your question isn't a HW question because you didn't actually want to learn any physics is not a good strategy to get people that like to teach physics (i.e. our experts here) on your side. We don't (or at least shouldn't) judge questions by taking guesses at what goes on in their askers mind, see my answer for more elaboration on this. – ACuriousMind Jun 28 '20 at 14:43
• @Mitsuko I'm talking about what you wrote in this meta question, specifically: "I wasn't interested in learning or understanding any physics methods; my interest was to find out whether 13 is indeed the answer for the problem in question." To me, this is suggesting that you wanted answers that were just "13 is correct". If you also want to see a solution along with it, you're still essentially looking for us to "help you understand the method by which the question can be solved"; even if you have no actual intention of learning from that solution. – JMac Jun 28 '20 at 14:51

I can't for the life of me understand why you guys closed that question. It was very interesting and popular. It seems unless someone already knows how to solve the problem, this site doesn't want them to ask a question. How do we "vote to reopen"

• As for the majority of your answer, it's been explained in great detail in other answers why the question got closed. And you can only vote to reopen if your reputation on Physics SE is greater than (or equal to) 3k. – user258881 Jun 29 '20 at 9:41
• ... did you read any of the answers to this question? Several people explain their take on the situation and why they might vote to close as homework. – JMac Jun 29 '20 at 13:27
• Yes, they're answers had trivial complaints such as "Wasn't about a physics concept" when there are tons of concepts at play. And also about the fact that "there was no work shown". Which is debatable, but also why you get my critique " unless someone already knows how to solve the problem, this site doesn't want them to ask a question" – Bobak Hashemi Jun 29 '20 at 17:19
• A question having physics concepts at play is not the same thing as asking about physics concepts, which the OP explicitly said they were not interested in. – BioPhysicist Jun 29 '20 at 17:27
• @BobakHashemi What do you mean "unless someone already knows how to solve the problem, this site doesn't want them to ask a question"? Those two things aren't necessarily related. The fact that people here can solve the question doesn't mean it's suitable for the site. People have shown solutions to the problem, but a lot of people in the community don't want to see homework-like questions, and there is a strong case that this falls under that category. – JMac Jun 29 '20 at 21:56
• A homework problem should not be considered any problem where you haven't isolated a single concept. By your logic, if I say "how do I find the energy states of this system ," that wouldn't be appropriate for this site, yet MANY MANY such questions exist on this site. The point it all of this is arbitrary. There's no hard and fast definition of a "homework problem." The question removed was on pace to be the top question of the month (already the second most popular), so I don't wanna hear that "a lot of people in the community didn't want it". – Bobak Hashemi Jun 29 '20 at 23:33
• I post on this site for 2 reasons. 1. To keep my skill sharp, 2. to help others learn. I bet you a lot of people are like me, and you guys are killing point (2). Where on the internet is the right place to ask how to solve a physics problem? Go to any of the other stackexchanges, there are tons of questions about "how do I do this". If we want to remove "low effort questions" I am all for it, but this question was high effort, very interesting, and it's solution could be extremely pedagogical for a student studying CM. This is why it's easier to learn computer science than physics. – Bobak Hashemi Jun 29 '20 at 23:36
• @BobakHashemi What was "high effort" about the question? There was no work shown towards the actual problem, or any concepts addressed. Most of the question is just explaining the setup and the story of how they heard the problem. – JMac Jun 30 '20 at 3:28
• This is why it's easier to learn computer science than physics Physics SE isn't the only place to learn physics, and it doesn't claim or try to be. The users of the site decided a while ago that this site should not be a homework help site. As such, we have to try to be a little stricter on this point since it would be so easy for PSE to become a homework help site if left unchecked. You are still free to help others learn physics here, and much teaching and learning still happens. – BioPhysicist Jun 30 '20 at 3:34
• Also, note that all stack exchange sites are different, so comparisons between them aren't valid here. – BioPhysicist Jun 30 '20 at 3:52
• That's a pretty poor example since it has only been open for 3 hours. However, I agree this question should also be closed, and I have voted as such. If you see a question that is open that should be closed, you should vote/flag it to be closed. You can always find examples that have "slipped through the cracks". If you find anymore, vote to close them. Don't just complain about them not being closed. – BioPhysicist Jun 30 '20 at 4:45
• If you don't like a completely voluntary thing, then stop doing it. There isn't a point in complaining about it. I am not very fond of Scrabble, but I am not going to go up to people playing Scrabble and start telling them why they shouldn't be playing Scrabble. I am just going to not play Scrabble and instead play games I enjoy more. In terms of physics education, I am also a physics tutor. I love physics education. But PSE is not the place for such questions one would ask a tutor. I don't think there is an issue with that. There is a place for everything. – BioPhysicist Jun 30 '20 at 19:08
• If you really want to change things here, then make a meta post proposing your change to the homework policy and how we should be handling such questions. – BioPhysicist Jun 30 '20 at 19:10
• @BobakHashemi The question contains no explanation for why the tube would jump. It doesn't talk or ask about any of the concepts involved, just "Is 13 the solution, and how would you solve it?". When you boil it down, it's a pretty basic "Give me the solution to this exercise" question, or a "Confirm this answer" question, neither of which are considered on topic by a large number of community members. – JMac Jun 30 '20 at 19:39
• @BobakHashemi That well could be a homework problem. That other question you linked to is indeed homework-like, and five people have voted to close it as such. – G. Smith Jun 30 '20 at 20:07