TextWatcher NullPointerException Failure
What is a NullPointerException, and how do I fix it?
prove $\sum_{i=1}^{n}(x_i-\bar{x})^2\lt\sum_{i=1}^{n}(x_i-a)^2$ How do we prove that $$ \sum_{i=1}^{n}(x_i-\bar{x})^2\lt\sum_{i=1}^{n}(x_i-a)^2 $$  where $a$ is any value other than $\bar{x}$, the arithmetic mean.  My Attempt: $$ \sum_{i=1}^{n}(x_i^2-2x_i\bar{x}+\bar{x}^2)\lt\sum_{i=1}^{n}(x_i^2-2x_ia+a^2)\\\sum_{i=1}^{n}x_i^2-2\bar{x}\sum_{i=1}^{n}x_i+\sum_{i=1}^{n}\bar{x}^2\lt\sum_{i=1}^{n}x_i^2-2a\sum_{i=1}^{n}x_i+\sum_{i=1}^{n}a^2\\-2\bar{x}.n\bar{x}+n.\bar{x}^2\lt-2a.n\bar{x}+n.a^2\\-2\bar{x}^2+\bar{x}^2\lt-2a\bar{x}+a^2\\-\bar{x}^2\lt-2a\bar{x}+a^2 $$ But how do I proceed further or is there any better way ? Four balls with different colors in a box, how many times do I need to pick to see all four colors? Round a double to x significant figures Example where $f\circ g$ is bijective, but neither $f$ nor $g$ is bijective Can anyone come up with an explicit example of two functions $f$ and $g$ such that: $f\circ g$ is bijective, but neither $f$ nor $g$ is bijective?  I tried the following: $$f:\mathbb{R}\rightarrow \mathbb{R^{+}} $$ $$f(x)=x^{2}$$  and  $$g:\mathbb{R^{+}}\rightarrow \mathbb{R}$$ $$g(x)=\sqrt{x}$$  $f$ is not injective, and $g$ is not surjective, but $f\circ g$ is bijective  Any other examples? Describe in English a Turing machine that semidecides the following language - Is this solution correct? The language being L, which is described as follows:  $L$ = { $&lt;M&gt;$ | $M$ accepts the binary encodings of at least 4 odd numbers } .  My solution:  M generates the binary encodings in $\Sigma_M*$ in ascending order and uses dovetailing to interleave the computation of M on those binary encodings. As soon as four computations accept, M halts and accepts.  Is this correct? What corrections would have to be made if not? I am not sure if I am providing enough details in my solution which may cause it to be incorrect. If no spell can reawaken the dead, how did the resurrection stone work? Dumbledore himself said that no spell can reawaken the dead. Isn't that the main objective of the resurrection stone? If one can't reawaken the dead then what is the use of the stone? Surely then one of the Hallows is flawed? Sci-Fi Movie/Show Where a Soul is Captured in a Glass Vessel The other day I was trying to download something for Minecraft and it involved my bin folder. So I was looking for it and couldn't find it. I then thought that I might have accidentally deleted it, but didn't find it in the trash. I have no idea how to get the bin folder back with all the Minecraft binary files in them. polar decomposition of a square A when A is not full rank/invertible Create model from XYZ data points How to resolve error "Handle bad layers" in QGIS? I'm new to QGIS and have been seeing what it can do for me – seems good. I imported shape file data from a UK Ordnance Survey data file and saved the file in a new folder. It was very good, doing all I wanted. I exported and got exactly what I wanted ( a tiff image).   I closed the file in order to try a new experiment. When I went to re-open it I got a dialogue box saying 'Handle Bad Layers. I don't understand what is at issue and what to do. Error: Account is Not Allowed To Suggest Edits I get this message while trying to edit a post on SuperUser while using the iOS mobile app. I have at least 101 reputation on SU, more than enough to be able to edit posts. This appears to be a bug. Difficulty in finding a counterexample This isn't a particularly major issue, but I've had this thing nagging me for a while. When looking at QGIS 3.4's global variables, user_full_name is assigned my given and surname, which includes a diaeresis (¨) somewhere in there. I can't seem to find any way to get QGIS to switch/adapt encoding and display the name correctly. The accented character gets switched to that ubiquitous black rhombus.  I looked for info on this behavior and found moderately similar issues like  and  but it's not exactly the same problem as it's not a geodata encoding issue but rather how QGIS deals with values pulled from the OS.  I have tried unchecking the Override system locale tickbox in Options|General as I prefer to use American English even though my OS is set to Canadian French. No effect to observe.  There's somewhat of a workaround right now which is to fix the name in the Project variable project_author as it is editable (it's filled with the offending global variable by default).  I'm curious to know, though, if someone has encountered this before and if there's a solution in QGIS. X,Y,Z missing in F3 When I press F3 to see the debug screen in I use Minecraft 1.8.1, some information is missing.   Most notably, there are no X, Y, Z coordinates.     What happened to my debug overlay? Possible Duplicate:           My name is Greg — this is Greg 's post.  If my name ended with an 's', I am aware of the proper apostrophe usage (James&nbsp;→ James'), but how should this be pronounced?  Phonetically, am I Jameses best friend or James best friend? Fluent and Query Expression — Is there any benefit(s) of one over other? LINQ is one of the greatest improvements to .NET since generics and it saves me tons of time, and lines of code.  However, the fluent syntax seems to come much more natural to me than the query expression syntax.  var title = entries.Where(e =&gt; e.Approved)     .OrderBy(e =&gt; e.Rating).Select(e =&gt; e.Title)     .FirstOrDefault();  var query = (from e in entries              where e.Approved              orderby e.Rating              select e.Title).FirstOrDefault();   Is there any difference between the two or is there any particular benefit of one over other? Find four groups of order 20 not isomorphic to each other. I have been there first time.   The reason why I think this might not be natural is that the expression "first time" seems to describe "past". You do not use the present perfect with an adverb indicating "past", in my understanding.  However, I feel the phrase below is not that funny.     This is the first time that I have been there.   I am wondering about the relationship between "the first time" and "I have been there". "That" could behave like a relative adverb. If that is the case, the antecedent of "that"—"the first time"—is shared with the following clause: "I have been there". Then, is it OK to say "I have been there first time"?  By the way, Google searches for "" and " in the UK domain show just 33 hits for the first phrase and 10 hits for the second. What spell targets count for the Graviturgy Magic wizard's Gravity Well feature? The  feature from the  (EGtW, p. 185) triggers &quot;whenever you cast a spell on a creature&quot;, and has an effect &quot;if the target is willing to move, the spell hits it with an attack, or it fails a saving throw against the spell.&quot; It's not clear to me what kinds of spells can actually trigger this feature. Based on the singular phrasing of &quot;on a creature&quot; and the later use of the word &quot;target&quot;, I would normally read this as only applying to spells that explicitly target creatures (and perhaps only those with a single target, in contrast to the phrasing of the  feature of the  wizard, for example). However, spells that target a location can use the word target in a different sense (see ). What's actually going on here? Does this feature only work on targeted spells? Or does it function for area of effect spells as well? Or is this just an ambiguous phrasing that will rely on the DM's ruling?