Why there is no value for $x$ if $|x| = -1$?
Is there a number whose absolute value is negative?
Why is the gravitational force always attractive? Is there another way to explain this without the curvature of space time?   PS: If the simple answer to this question is that mass makes space-time curve in a concave fashion, I can rephrase the question as why does mass make space-time always curve concavely? Why is the first band on a resistor never black? I'm taking an electronic circuit analysis class, and I was asked to give the color of the 3rd band of a 1MΩ resistor. My answer was blue, thinking it could be black-brown-blue (01 * 1MΩ), but the automated quiz said the correct answer was green (brown-black-green).  So I did some research, thinking there were just multiple correct answers, and I read in a few places that the first band on a resistor is never black (0). Why is this? Does a black first band have some other meaning? It would really help me remember it if I knew the history or reasoning behind it.  This question has been answered. For further reading on zero-ohm resistors mentioned in the answers and comments here, I found these questions and answers helpful: I just bought a used  and it comes with regular rim brakes. I'm perfectly happy with them so far, but have been wondering if disc brakes would come handy when it rains.  What is involved in converting a bike from rim brakes to disc brakes (mechanical or hydraulic)?   Is this something that is feasible, or am I better off buying another bike that already has disc brakes? How many solutions has the equation $\sin x= \frac{x}{100}$ ? How can I find duplicate photos? What can I use to find duplicate photos, including photos that have been resized? ATMEGA328P standalone sketch doesn't work as expected How can I set the location (as it's picked up in CoreLocation services) in the iPhone Simulator? What is the difference between Ubuntu and its derivatives? What different Ubuntu derivatives are there? And what is special with them? Centering polygon on specific coordinates using QGIS I need to place a set of polygons onto a set of points, so that each polygon is centered on its corresponding point. How do I do that? In MapInfo I can just manually edit the coordinates of the center, but there does not seem to be an equivalent in QGIS. Why are the IV (constant) values fixed for HMAC/SHA? Why do HMAC/SHA IV's have a fixed value? I refer to the arbitrary H constants which are included in the algorithm prior to any data being fed in.  Why aren't they exposed to the user, so one can decide on an IV and modify it accordingly (for example, in java they are provided at hash function specification, instead of being supplied by the user at init)?  How does modifying these IVs affect the algorithm? I use babelbib and I have a source with two authors. Contrarily to when using the plain bib style, as soon as I switch to babplain, the author names are formatted like this:  [1] Müller, Jan und Eva Schulze: Name of the book, 2015.   While I would like both author names to be formatted the same way, that is one of these:  [1] Müller, Jan und Schulze, Eva: Name of the book, 2015. [1] Jan Müller und Eva Schulze: Name of the book, 2015.   sources:  % test.tex \usepackage[ngerman]{babel} \usepackage[fixlanguage]{babelbib} \selectbiblanguage{ngerman} \bibliographystyle{babplain} \bibliography{test}  % test.bib @manual{foo,     author = "Müller, Jan and Schulze, Eva",     title = "Name of the book",     year = "2015", }   I can fix it by specifying and {Schulze, Eva}, but that way all is treated as the last name, that cannot be the solution, can it? Can't execute terminal commands: "the command 'sudo' is available in '/usr/bin/sudo'" I have been using Ubuntu 12.04 for quite a while and have never had a problem come at me out of the blue like this. I'm trying to install python 3.2 on my Ubuntu system and every time I run the code to compile the python source, I get this error:  'Command 'sudo' is available in '/usr/bin/sudo' The command could not be located because '/usr/bin' is not included in the PATH environment variable. sudo: command not found'   I've also tried running gksudo command to view what my environment shows but I pretty much get the same error. Drush 6 works great of corse on a Drupal 6 website, but will I have all of the Drush 6 features when working on a Drupal 7 website? Should I use Drush 7 when working on a drupal 7 website?  I found this post that says you can switch between the two version easily, is this correct?  switch to drush6 command: composer global require drush/drush:6.*  switch to drush7 command: composer global require drush/drush:dev-master How to create a link to a URL provided in a bib file with custom text Using biblatex, how can I get a URL from the bib file so that I can use it in the \href command?  I am guessing that the \usefield command is what I am looking for and that in order to use that I would need the \entrydata command. But both are undefined.  \documentclass{article} \usepackage[backend=biber]{biblatex} \usepackage{hyperref}  \usepackage{filecontents} \begin{filecontents*}{sources.bib} @online{biblatex,     url = {http://mirrors.ctan.org/macros/latex/contrib/biblatex/doc/biblatex.pdf},     urldate = {2018-02-02}, } \end{filecontents*}  \addbibresource{sources.bib}  \begin{document}      % This would work, but I don't want to duplicate the URL from the bib file:     \href{http://mirrors.ctan.org/macros/latex/contrib/biblatex/doc/biblatex.pdf}{biblatex documentation}      % Does not work because \citeurl{biblatex} is already a link, not the URL:     %The \href{\citeurl{biblatex}}{biblatex documentation}      % Does not work because \usefield and \entrydata are undefined:     %The \entrydata{biblatex}{\usefield\href{url}{biblatex documentation}}      \printbibliography \end{document} How to show (or hide) a hidden file I wanted to add classpath to my JDK. While searching a way to do it I noticed everyone open .profile file using terminal. But when I want to open and edit it with a text editor I couldn't see that file in Home folder.  Can someone tell me why is this. And also if possible how can I access .profile in home folder the GUI way. Book series my dad told me about. It involves space travel, clones, and an indigenous people with kangaroo tails My dad read a book series that he recommended to me last year. Now that I am ready to start it, neither of us can recall the title. He said there were several in the series but he can't recall how many.   The book is about traveling to a new planet, presumably with the goal of colonizing it. The crew are clones who have no memory. I think the goal was for the older original versions of the clones to transfer their consciousness into the clone bodies to be able to live on the new planet but something goes wrong.   There is an indigenous species on the planet who are humanoid but have kangaroo like tails.   The clone crew has markings on them that they don't understand until late. Apparently they are markings to indicate status or role on the new world. The person who they voted as there leader, it turns out, is marked as a servant or slave class. How to get rid of blank pages in PDF exported from SSRS I have a two-page SSRS report. When I exported it to PDF it was taking 4 pages due to its width, where the 2nd and 4th pages were displaying one of my fields from the table. I tried to set the layout size in report properties as width=18in and height =8.5in.  It gave me the whole table in a single page of PDF, but I am still getting the 2nd and 4th pages blank.   Is the way I am doing it incorrect?  How else can I get rid of those blank pages? How to enter the Default Keyring password via the command line? Is there a way to enter the default keyring password using the command line?   For instance:  You have a remote setup of Ubuntu 10.10 thats set to auto login. You don't want to remove  the keyring password.  All right the system boots up and logs in automatically, then asks for the keyring password now at this point you can create ssh connections but you can't remote desktop.   What can you do to enter the keyring password at this point?  Also, to better clarify, this is from a remote connection using the command line. I write financial applications where I constantly battle the decision to use a double vs using a decimal.  All of my math works on numbers with no more than 5 decimal places and are not larger than ~100,000. I have a feeling that all of these can be represented as doubles anyways without rounding error, but have never been sure.  I would go ahead and make the switch from decimals to doubles for the obvious speed advantage, except that at the end of the day, I still use the ToString method to transmit prices to exchanges, and need to make sure it always outputs the number I expect. (89.99 instead of 89.99000000001)  Questions:   Is the speed advantage really as large as naive tests suggest? (~100 times) Is there a way to guarantee the output from ToString to be what I want? Is this assured by the fact that my number is always representable?   UPDATE: I have to process ~ 10 billion price updates before my app can run, and I have implemented with decimal right now for the obvious protective reasons, but it takes ~3 hours just to turn on, doubles would dramatically reduce my turn on time. Is there a safe way to do it with doubles? Switch statement fallthrough in C#?