Why is the squared difference so commonly used?
Why square the difference instead of taking the absolute value in standard deviation?
How to resolve conflicting distributions in apt-get When doing an apt-get update/upgrade I see that warning  W: Conflicting distribution: https://downloads.plex.tv/repo/deb public InRelease (expected public but got )   I was upgrading to Ubuntu Zesty 17.04 before and do not know how to fix the above. Already have seen ? but there are no suggested fixes for that.  Maybe one of you can give some hints? Thanks! Given two sets $A$ and $B$, what is the difference between $A + B$ and $A \cup B$? For example, if $A = \left\{ a, b, c \right\}$ and $B = \left\{ d, e, f \right\}$, what are $A + B$ and $A \cup B$, respectively? Area of a quadrilateral proof Optimal step size in gradient descent Is there a way to install a newer version than in the repository?  Ubuntu installs vagrant 1.4.3 at the moment, but I need at least 1.5 I just added a PPA repository for the development version of the GIMP, but I get this error:  $ apt-get update &amp;&amp; apt-get upgrade ... The following packages have been kept back:   gimp gimp-data libgegl-0.0-0 libgimp2.0   Why and how can I solve it so that I can use the latest version instead of the one I have now? Animagi (Sirus specifically) and wands? What is the expression on RegularExpressionValidator to check if the Textbox text is 6 or more characters long? Grammatically, what is "It" in the following sentence? I'm currently working at a private academy in Korea, and my boss just asked me a real head-scratcher.   In the sentence:     It doesn't have to be hot and humid for players to lose too much water from their bodies.    I'm aware that "It" is a subject pronoun replacing "The weather." Besides that, however, I'm unsure.   Is it a false subject? I wouldn't think so since it's a pronoun. Is it some crazy kind of indirect object?  Anyway, thank you all for your help! I've only found a recursive algorithm of the extended Euclidean algorithm. I'd like to know how to use it by hand. Any idea? Storing third-party libraries in source control Should libraries that the application relies on be stored in source control? One part of me says it should and another part say's no. It feels wrong to add a 20mb library that dwarfs the entire app just because you rely on a couple of functions from it (albeit rather heavily). Should you just store the jar/dll or maybe even the distributed zip/tar of the project?  What do other people do? How to show  that $\mathbb{Z}[i]/I$ is a finite field whenever $I$ is a prime ideal? Is it possible to find the cardinality of $\mathbb{Z}[i]/I$ as well?  I know how to show that it is an integral domain, because that follows very quickly. CSS Display an Image Resized and Cropped I want to show an image from an URL with a certain width and height even if it has a different size ratio.  So I want to resize (maintaining the ratio) and then cut the image to the size I want.  I can resize with html img property and I can cut with background-image.  How can I do both?  Example:  This image:     Has the size 800x600 pixels and I want to show like an image of 200x100 pixels   With img I can resize the image 200x150px:  &lt;img      style="width: 200px; height: 150px;"      src="http://i.stack.imgur.com/wPh0S.jpg"&gt;    That gives me this:    &lt;img style="width: 200px; height: 150px;" src="https://i.stack.imgur.com/wPh0S.jpg"&gt;       And with background-image I can cut the image 200x100 pixels.  &lt;div      style="background-image:            url('https://i.stack.imgur.com/wPh0S.jpg');      width:200px;      height:100px;      background-position:center;"&gt;&amp;nbsp;&lt;/div&gt;    Gives me:        &lt;div style="background-image:url('https://i.stack.imgur.com/wPh0S.jpg'); width:200px; height:100px; background-position:center;"&gt;&amp;nbsp;&lt;/div&gt;      How can I do both?  Resize the image and then cut it the size I want? How to compute the  formula $\sum  \limits_{r=1}^d r \cdot 2^r$? Given $$1\cdot 2^1 + 2\cdot 2^2 + 3\cdot 2^3 + 4\cdot 2^4 + \cdots + d \cdot 2^d = \sum_{r=1}^d r \cdot 2^r,$$ how can we infer to the following solution? $$2 (d-1) \cdot 2^d + 2. $$   Thank you I've always been taught to put myself last when referring to myself in the same sentence as others but the usage of "me and..." seems to be everywhere these days. The misuse of the word "me" instead of "I" aside, is there some new rule I haven't heard of? Shouldn't we put ourselves last regardless of the "me"/"I" usage?  Examples of "correct" usage:      My friends and I went for some ice   cream. Did you see my friends and me   at the ice cream stand?   Examples of "incorrect" usage:     Me and my friends went for some ice   cream. Did you see me and my friends   at the ice cream stand?   Note: I was also taught that the only person who could put themselves first was the queen. Password Protect QGIS project On a shared computer, I have a QGIS project which links up to a PostGIS database that contains my data. If a user wants to access layers from the db, they have to enter the db credentials, so that's OK.   However, I have previously logged on and imported layers from my db into QGIS, and manipulated them in QGIS (styling options based on meta-data, etc.)... Anybody who opens my QGIS project can view these layers in QGIS, and can therefore see the data I wish to be protected in my db.  Is there a way to password protect my QGIS project? According to this question:  entire ruSO site shouldn't become hot. But I just saw the following while searching MSE:        Direct link to the question on ruSO:   Perhaps the HNQ filter works on question title (in the current case there are no non-Latin symbols) instead of site origin. Hence, according to the post mentioned before this behaviour should be interpreted as a bug.   However, I suggest to fix such "bug" by taking another feature request in mind: Solve differential equation:  $x'=x^2- \frac{2}{t^2}$  Maybe is it sth connected with homogeneous equation? I have no idea how to solve it. Why doesn't Doctor Strange remove the Infinity Gauntlet from Thanos? Doctor Strange seemingly has the ability to open portals wherever he wants. We see at the beginning of Infinity War what happens when he closes a portal and someone isn't fully through it.  Is there any reason why he can't open a portal around the left-elbow of Thanos, and then close it?  I realize that Thanos probably wouldn't allow this to happen normally,      but when he is mostly asleep, and Tony and Spider-Man are pulling on the gauntlet, Doctor Strange has ample opportunity, and plenty of space to just sever Thanos' arm.   Why doesn't he? Ubuntu desktop 18.04 LTS freezes with USB WiFi dongle OS: Ubuntu desktop 18.04 LTS Linux version 4.15.0-24-generic  USB WiFi: odroid WiFi Module 3 with Realtek RTL8188CUS-GR  syslog has only ^@  Jul  4 12:31:50 udbv-HP-ProBook sudo: pam_ecryptfs: pam_sm_authenticate: /home/udbv is already mounted ^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^$ Jul  4 12:33:30 udbv-HP-ProBook systemd-modules-load[396]: Inserted module 'ppdev' Jul  4 12:33:30 udbv-HP-ProBook systemd-modules-load[396]: Inserted module 'parport_pc' Jul  4 12:33:30 udbv-HP-ProBook systemd-cryptsetup[424]: crypt_init() failed: Block device required Jul  4 12:33:30 udbv-HP-ProBook systemd[1]: Starting Flush Journal to Persistent Storage... Jul  4 12:33:30 udbv-HP-ProBook swapon[415]: swapon: /swapfile: read swap header failed Jul  4 12:33:30 udbv-HP-ProBook systemd[1]: Started Create Static Device Nodes in /dev. Jul  4 12:33:30 udbv-HP-ProBook systemd[1]: Starting udev Kernel Device Manager... Jul  4 12:33:30 udbv-HP-ProBook systemd[1]: Started Set the console keyboard layout. Jul  4 12:33:30 udbv-HP-ProBook systemd[1]: Reached target Local File Systems (Pre). Jul  4 12:33:30 udbv-HP-ProBook systemd[1]: Mounting Mount unit for vlc... Jul  4 12:33:30 udbv-HP-ProBook systemd[1]: Mounting Mount unit for gnome-3-26-1604... Jul  4 12:33:30 udbv-HP-ProBook systemd[1]: Mounting Mount unit for gnome-calculator... Jul  4 12:33:30 udbv-HP-ProBook systemd[1]: Mounting Mount unit for pycharm-community... Jul  4 12:33:30 udbv-HP-ProBook systemd[1]: Mounting Mount unit for gnome-3-26-1604... Jul  4 12:33:30 udbv-HP-ProBook systemd[1]: Mounting Mount unit for skype, revision 41... Jul  4 12:33:30 udbv-HP-ProBook systemd[1]: Mounting Mount unit for gnome-calculator... Jul  4 12:33:30 udbv-HP-ProBook systemd[1]: Mounting Mount unit for gnome-calculator... Jul  4 12:33:30 udbv-HP-ProBook systemd[1]: Mounting Mount unit for skype, revision 38... Jul  4 12:33:30 udbv-HP-ProBook systemd[1]: Mounting Mount unit for pycharm-community... Jul  4 12:33:30 udbv-HP-ProBook systemd[1]: Mounting Mount unit for vlc... Jul  4 12:33:30 udbv-HP-ProBook kernel: [    0.000000] microcode: microcode updated early to revision 0x84, date = 2018-01-21   I tried following  but it didn't help.  Any ideas?