How is the following differential equation solved?
How are second order nonlinear ordinary differential equations solved?
Why is using "for...in" for array iteration a bad idea? Prove that $R$ is a commutative ring if $x^3=x$ Let $R$ be a ring satisfying: $\forall x\in R, \; x^3=x$. Prove that $R$ is a commutative ring. How does negation affect the use and understanding of "or" and "and" I'm trying to make more sense of how negation effects how a sentence is parsed and understood if and's and or's are used within them.  Pop quiz: You are trapped on a bus with a bomb going 50 MPH. You have a radio... (okay enough Keanu Reeves references) :-)  Let's say the bomb expert says "Don't cut the red or green wires." I think that means "Do not cut the wires colored red. Do not cut the wires colored green."  Now, let's say the bomb expert said on the radio "Do not cut the red and green wires", instead. Do I take that to mean:     "Do not cut the wires colored red. Do not cut the wires colored green."   OR     "Do not cut the wires whose insulation has red and green stripes." ?   OR     "It's okay to cut the wires colored red or the wires colored green, as long I don't cut one of each color."   Which meaning should I take if the radio breaks and I can't ask follow up questions? If "No One" uses a face from the Hall of Faces to become someone then how did he do this How Deep Are Bender's Insides? Bender often pulls large objects from his torso cupboard, but how deep or how much empty space is he capable of storing? Can he bend space around the perimeters of the frame of his torso's door? If that is the case, does it also bend time? I suppose he might bend in more ways than one... I know $4p^4+1$ can't be square number, cause $4p^4&lt;4p^4+1&lt;4p^4+4p^2+1$ for all natural number p. But I don't know the way to prove $3p^4-3p^2+1$ can(not) be square number. Is there a well known way to prove it? How do I include lines in resolv.conf that won't get lost on reboot? How do I use the latest GCC on Ubuntu? I want to compile my program with the latest version of gcc.  Ubuntu 14.04 comes with gcc 4.8.2, however there's 4.9.0 available, moreover, I see that it is available as a package: . I tried to install it  sudo apt-get install gcc-4.9   but it says  Reading package lists... Done Building dependency tree        Reading state information... Done Note, selecting 'gcc-4.9-base' for regex 'gcc-4.9' gcc-4.9-base is already the newest version. 0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.   Looks like it is already installed, just not as the default one? How do I utilize it to build my program? Maybe this is an easy question, maybe not.  I have a select box where I hardcode with width. Say 120px.    &lt;select style="width: 120px"&gt;   &lt;option&gt;REALLY LONG TEXT, REALLY LONG TEXT, REALLY LONG TEXT&lt;/option&gt;   &lt;option&gt;ABC&lt;/option&gt; &lt;/select&gt;     I want to be able to show the second option so that the user can see the full length of the text.  Like everything else.  This works fine in Firefox, but doesn't work with Internet Explorer6. Can I use Mage Hand to fly by Polymorphing myself and picking myself up with the hand? Could I first cast Mage Hand, then Polymorph into a Tiny creature less than 10 pounds then use the Mage Hand to pick myself up and fly at 30 Ft per turn?  Polymorph says:     The new form can be any beast ... The target's game statistics,   including mental ability scores, are replaced by the statistics of the   chosen beast. It retains its alignment and personality ... The   creature is limited in the actions it can perform by the nature of its   new form and it can't speak, cast spells, or take any other action   that requires hands or speech.   This keeps me from casting spells, which keeps me from just casting Mage Hand to fly as long as I want to over and over. But for that initial duration of the Mage Hand cantrip, could I use the Mage Hand to fly as a Tiny polymorphed creature until the spell runs out? Boxplot interpretation: is it correct that a boxplot is missing a whisker? Why is the QGIS map composer grid showing unreasonable lat/lon? I need to print a map with coordinates in the format of Degree, Minute and second. CRS is set to WGS 84 (EPSG 3857) for both layers and on the project properties it is set to enable transformation on the fly. But then, when in map composer I get the following coordinates, which make no sense to me. best way to pick a random subset from a collection? I have a set of objects in a Vector from which I'd like to select a random subset (e.g. 100 items coming back; pick 5 randomly). In my first (very hasty) pass I did an extremely simple and perhaps overly clever solution:  Vector itemsVector = getItems();  Collections.shuffle(itemsVector); itemsVector.setSize(5);   While this has the advantage of being nice and simple, I suspect it's not going to scale very well, i.e. Collections.shuffle() must be O(n) at least. My less clever alternative is  Vector itemsVector = getItems();  Random rand = new Random(System.currentTimeMillis()); // would make this static to the class      List subsetList = new ArrayList(5); for (int i = 0; i &lt; 5; i++) {      // be sure to use Vector.remove() or you may get the same item twice      subsetList.add(itemsVector.remove(rand.nextInt(itemsVector.size()))); }   Any suggestions on better ways to draw out a random subset from a Collection? What is the easiest way to make a backup of an entire hard disk I got myself a dell laptop from the local computer store. Its a used machine with Windows Vista Home Basic on it. I want to load Ubuntu Desktop 10.10 though so I can do perl development. BUT I want to keep a copy of the entire harddrive with the dell utility partition and Windows Vista in case I want to go back. I was thinking I could image the drive but I not sure what to use, I don't have Ghost or anything, Someone had told me about Clonezilla. Would that work for me? Is it hard to use? Also I want to burn the data to a DVD or something more storable than a harddisk. Android: Making Https Request How to give different permissions to multiple groups of users? I installed Ubuntu 12.04 server and want to give full folder access say example: "Folder01" to group "Group01' and Limit "Group02" for read access only. How I can do this. A lot of people write makefiles that say something like  paper.pdf: paper.tex         pdflatex paper         bibtex paper         pdflatex paper         pdflatex paper   To handle re-running TeX to get new/changed references and so forth. Is there a better way to do this? My phone was stolen last night. I made sure it was in Lost Mode in iCloud and it was immediately in Offline status when I open iCloud. I am positive the thief switched it off. Now I am 100% certain the Find my iPhone option was turned on on my iPhone, but will the "Lost Mode" be of any help if it was not turned on on the iPhone? Would it be showing "Offline" if I did not turn on the option? Switching between virtual console and GUI How to switch between virtual console and GUI in Ubuntu? I wanted to see what key functions would allow me to switch between the two. How to round pixel values of a raster in QGIS? I have a raster with float number values for example: 2.544459104537964 and I want to round these up to integers. I have seen other posts on ArcGIS like  but when I use Raster Calculator in QGIS, Int(myraster + 0.5) only makes the first value (which is 0) to 0,5 and the last one (which is 100) to 100,5. The other pixels stay float.