RHCE equivalent for Ubuntu
Is there such a thing as a Ubuntu Certified Engineer?
Let $x$ and $y$ be positive integers such that $xy \mid  x^2+y^2+1$. Show that $$ \frac{x^2+y^2+1}{xy}= 3 \;.$$ I have been solving this for a week and I do not know how to prove the statement. I saw this in a book and I am greatly challenged. Can anyone give me a hint on how to attack the problem? thanks Understanding my electrical panel I just purchased .  I'll be installing it in my RV.  Current will be supplied by a 12VDC to 120VAC, 3000W inverter.  I'll be using Single-Pole Type BR breakers.  Here's a picture of the box:    My current understanding is that I must install a grounding bar to the box.  This is my current understanding of how to connect the breaker to the main supply.:    Here is my understanding of how I would wire in new circuits:    Does this look right?  I would really appreciate your help -- I've been beating myself over the head about this. Is there an overall view of your cities? Video showing up as white space On  question, there is a YouTube video in , on the Android app the video shows up as a white space. There is no indication that it is a video.  Would it be possible to show the video in the app or link to the video on YouTube instead? Visa for Istanbul trip during layover I am an Indian (Indian Passport) presently in Kano, Nigeria on a business visa. I am going back to Mumbai on 22 Sept by Turkish Airlines with a 12 hour layover time in Istanbul.  We plan to see the city during this time.  Can I get a visa on arrival? A "failed to fetch" error occurs when apt-get update is run. How do I fix this? In naive set theory, I believe ∅ = {∅} = {{∅}} is correct, but just wanted to make sure that I understood this correctly.   ∅ is an empty set, so having an empty set as an element of a set that contains nothing else is pretty much the same thing as e.g. marking the number 2 as 2.000000, right? Doesn't the symbol ∅ intrinsically imply that this is an empty set which contains it self? Error: "To run a ssis package outside of sql server data tools you must install [send successful email] of Integration Services or higher." NOTE that the title of this qusetion is a verbatim error message specific to this user. The error message illustrates a bug in the dtexec application, which substitutes a user variable into the error message string. In this case, the standard message Standard E dition is replaced with send successful email.  The 'standard' error message would be :  Description: To run a SSIS package outside of Business Intelligence Development Studio you must install Standard Edition of Integration Services or higher.    Version SSIS 2012. Package was originally 2005 ver. Package on file system.  DB Engine / Agent on Host 1, SSIS on Host 2.  Execution from Host 2 runs successfully. Execution from Host 1 gives the error in the question subject. Saw , but engine and agent are installed on Host 1. Has anyone seen this? Google returns no results when searching on the exact error (subject line is exact, wording is odd in the error message).  Thank you! Solving "mv: Argument list too long"? I want to buy a home, but I'm not interested in using a realtor as a buyer's agent.  I know that in MLS systems, when a realtor lists a house they specify what commission a buyer's agent will be paid.  Since I am the one who is bringing a qualified buyer to the listing agent, I feel that I would should get the commission (even if it is in the form of a discount on the house).    Essentially, the seller would get the same amount of money at closing... the listing agent would get the same commission as they normally would for showing the house to someone with a buyer's agent... but I would pay less for the house.  Is there a tactful way to negotiate this with the listing realtor?  For example, should I make a side contract with the realtor to pay me the commission at closing?  Or perhaps I can specify in my offer that they should reduce their fees to the seller by the commission amount if the offer is accepted, in order to make my offer more attractive?  Are these types of deals ever done, and if so, is there a conventional way to make it happen?  Thanks g++ undefined reference with a shared library QR Codes generation from MySQL rows Facebook message notification showing blank message Since I updated the system to 10.11.5, the Facebook message notification is not showing message text.   Is this a bug in this software upgrade of OSX? What is the physical meaning of commutators in quantum mechanics? This is a question I've been asked several times by students and I tend to have a hard time phrasing it in terms they can understand. This is a natural question to ask and it is not usually well covered in textbooks, so I would like to know of various perspectives and explanations that I can use when teaching.  The question comes up naturally in what is usually students' second course in quantum physics / quantum mechanics. At that stage one is fairly comfortable with the concept of wavefunctions and with the Schrödinger equation, and has had some limited exposure to operators. One common case, for example, is to explain that some operators commute and that this means the corresponding observables are 'compatible' and that there exists a mutual eigenbasis; the commutation relation is usually expressed as $[A,B]=0$ but no more is said about that object.  This naturally leaves students wondering     what is, exactly, the physical significance of the object $[A,B]$ itself?   and this is not an easy question. I would like answers to address this directly, ideally at a variety of levels of abstraction and required background. Note also that I'm much more interested in the object $[A,B]$ itself than what the consequences and interpretations are when it is zero, as those are far easier and explored in much more depth in most resources.    One reason this is a hard question (and that commutators are such confusing objects for students) is that they serve a variety of purposes, with only thin connecting threads between them (at least as seen from the bottom-up perspective).   Commutation relations are usually expressed in the form $[A,B]=0$ even though, a priori, there appears to be little motivation for the introduction of such terminology. A lot of stock is placed behind the canonical commutation relation $[x,p]=i \hbar$, though it is not always clear what it means.  (In my view, the fundamental principle that this encodes is essentially de Broglie's relation $\lambda=h/p$; this is made rigorous by the  but that's quite a bit to expect a student to grasp at a first go.) From this there is a natural extension to the Heisenberg Uncertainty Principle, which in its general form includes a commutator (and an anticommutator, to make things worse). Canonically-conjugate pairs of observables are often introduced, and this is often aided by observations on commutators. (On the other hand, the energy-time and angle-angular momentum conjugacy relations cannot be expressed in terms of commutators, making things even fuzzier.) Commutators are used very frequently, for example, when studying the angular momentum algebra of quantum mechanics. It is clear they play a big role in encoding symmetries in quantum mechanics but it is hardly made clear how and why, and particularly why the combination $AB-BA$ should be important for symmetry considerations.  This becomes even more important in more rigorous treatments of quantum mechanics, where the specifics of the Hilbert space become less important and the algebra of observable operators takes centre stage. The commutator is the central operation of that algebra, but again it's not very clear why that combination should be special. An analogy is occasionally made to the Poisson brackets of hamiltonian mechanics, but this hardly helps - Poisson brackets are equally mysterious. This also ties the commutator in with time evolution, both on the classical side and via the Heisenberg equation of motion.   I can't think of any more at the moment but they are a huge number of opposing directions which can make everything very confusing, and there is rarely a uniting thread. So: what are commutators, exactly, and why are they so important? Ubuntu touchpad issues - mouse pointer jumps around Can "THAT" be omitted here? So we can say   "Do you think (that) he'll come?"   (in other words, we can omit THAT in conversation)  But what about with a sentence like   "Did he deny （that） he went to Thailand?"   Can "that" also be omitted like in the sentence above? All Faces to Individual Objects I am looking for a way to take all the faces of an object and make each face it's own object.   In the image above, you'll see a basic representation of what I'm trying to accomplish. On the left is a shape with faces, all attached. On the right is the result I want, an object for each face. The project I'm working on is much more complicated than this example, so I can't select each face and separate by selection. I have over 3,000 faces to work on. Would a compass with unmagnetized needle work? We know that the needle that is used in a compass is a permanently magnetized ferromagnetic material and commonly steel is used.  If we used an unmagnetized iron needle instead, would it still align with Earth's magnetic field lines? If yes, how? Implied string comparison, 0=='', but 1=='1' $x_{1}...x_{n}$ are independent continuous random variables with common distribution function $F(x)$,consider the order statistics $(x_{(1)},...,x_{(n)})$, compute $E(F(x_{(n)})-F(x_{(1)}))$  I have no idea to this problem, anyone could help me? Thanks!