JavaScript Regular Expression Email Validation
How to validate an email address in JavaScript
Proving the identity $\sum_{k=1}^n {k^3} = \big(\sum_{k=1}^n k\big)^2$ without induction I recently proved that  $$\sum_{k=1}^n k^3 = \left(\sum_{k=1}^n k \right)^2$$  using mathematical induction.  I'm interested if there's an intuitive explanation, or even a combinatorial interpretation of this property. I would also like to see any other proofs. I have a NOPASSWD line in /etc/sudoers (edited with visudo)  gatoatigrado    ALL=(ALL) NOPASSWD: /bin/set-slow-cpufreq   However, the output is,  gatoatigrado@coral:~&gt; sudo -n /bin/set-slow-cpufreq sudo: sorry, a password is required to run sudo   This kind of command works on an OpenSuSE machine, but not on Ubuntu 11.10. What am I doing wrong?  Note: I cannot find any relevant system log messages, e.g. via tail -f /var/log/syslog.  edit  Here is /etc/sudoers.  Defaults    env_reset  # things I've tried copying from an opensuse machine Defaults always_set_home Defaults env_keep = "LANG LC_ADDRESS LC_CTYPE LC_COLLATE LC_IDENTIFICATION LC_MEASUREMENT LC_MESSAGES LC_MONETARY LC_NAME LC_NUMERIC LC_PAPER LC_TELEPHONE LC_TIME LC_ALL LANGUAGE LINGUAS XDG_SESSION_COOKIE"  root    ALL=(ALL:ALL) ALL gatoatigrado ALL=NOPASSWD: /bin/set-slow-cpufreq %admin ALL=(ALL) ALL %sudo   ALL=(ALL:ALL) ALL Lowering elevation of lake using QGIS I am in QGIS. I have a raster layer of mountains and a lake. I have a vector layer (shapefile) of the lake. It sits nicely where it supposed to be over the raster level. I am going to convert this height map to an STL so that I can cnc this out of wood, so I'd like the actual lake to be something like 200 feet lower than it shows on the raster layer so that I can fill it with blue epoxy. I have read a lot of clipping and everything else, and I am lost. My Prof wrote that   $\sum_{n=2}^{\infty} n(n-1)x^{(n-2)} = \frac{2}{(1-x)^3}$  when $-1&lt; x&lt;1$  I do not understand where the above formula comes from. Can someone please explain the steps or provide a hint?   Thanks! Clearing NSUserDefaults I'm using +[NSUserDefaults standardUserDefaults] to store application settings. This consists of roughly a dozen string values. Is it possible to delete these values permanently instead of just setting them to a default value? By conservation of energy, the solid is left in a lower energy state following emission of a photon.  Clearly absorption and emission balance at thermal equilibrium, however, thermodynamic equilibrium is a statement of the mean behaviour of the system, not a statement that the internal energy is constant on arbitrarily short timescales.  The energy has to come from somewhere during emission, and go somewhere during absorption.  Energy in a solid can be stored as kinetic and potential energy of electrons and nuclei, either individually or in collective modes such as phonons and plasmons.  In thermal equilibrium energy will be stored more or less in various forms depending on the temperature and material.  However, even if most of the thermal energy in a particular solid at temperature $T$ is stored in the form of phonons, it could be that phonons primarily interact with light indirectly via electrons, e.g. a phonon excites an electron in a phonon-electron interaction, which can interact with light via the EM field.  Given that light is an EM field, it makes sense to me that it is emitted and absorbed by charged particles.  The electron-photon interaction is probably dominant for visible and ultraviolet light, given that metals are opaque, while semiconductors and insulators are transparent to (visible and UV) light with energy lower than their bandgap. However, once you get into energies in the IR and below, or X-rays and above, other mechanisms apparently take over.  For example, on the high-energy end of the spectrum I've heard that gamma rays can interact directly with nuclear degrees of freedom, which is reasonable considering that gamma rays are emitted during a lot of nuclear reactions.  A review of  might give clues to important light-matter interactions over a broad range of wavelengths.  Whether all of the these processes are involved in blackbody emission is a somewhat different question.  What physical processes mediate energy transfer during blackbody emission, and in which energy ranges are the various processes dominant? BootChamp no longer works on El Capitan, what's the fastest way to boot into Windows? During my studying to integration I find this integration.  So I tried to prove but I got stuk.  So I need help in this integration.  $$\displaystyle\int_{-\infty}^{\infty} \frac{x \sin (x)}{1+x^2}  dx = \frac {\pi}{e} $$ setuid root does not work Objective : Run a program as root (C++ binary). The same as :   And :   ./a.out output:  E: Could not open lock file /var/lib/dpkg/lock - open (13: Permission denied) E: Unable to lock the administration directory (/var/lib/dpkg/), are you root? psurana  //output for "whoami" Look below for the code.   ls -l output:  -rwsrwxr-x 1 root    root    46136 Jun  7 20:13 a.out  The Code :   #include &lt;string&gt; #include &lt;stdlib.h&gt; int main(int argc, char *argv[]){         std::string input = "apt-get install " + std::string(argv[1]);         system(input.c_str());         system("whoami");         return 0; }   Details: : compiled the program and then did chown root:root a.out &amp;&amp; chmod u+s a.out. Please look above for ls -l output.  I still do not get the root privileges and the output for system("whoami") in the code is my own username on the machine.  Reading the two linked questions did not yield me anywhere. :(. both the creator and the owner of the file are root. The setuid bit is set, so it should work. The filesystem is not external either, it is my own machine. How can I make this work? What are the “spam” and “rude or abusive” (offensive) flags, and how do they work? PHP parse/syntax errors; and how to solve them I wanted to use my android phone as a proxy server, meaning that I wanted to be able to use the IP on the phone as a proxy, so all request and response are received on the phone and forwarded back to the original requestor. How do I do this? In D&amp;D 5e &quot;&quot; is a condition that can affect a creature during the first round of combat, only until the end of their turn:  [... T]he GM compares the Dexterity (Stealth) checks of anyone Hiding with the passive Wisdom (Perception) score of each creature on the opposing side. Any character or monster that doesn’t notice a threat is surprised at the start of the encounter. If you’re surprised, you can’t move or take an action on your first turn of the combat, and you can’t take a reaction until that turn ends. A member of a group can be surprised even if the other members aren’t. - PHB 189  Does the action that causes the surprise count as part of the round, though? Say Renee, a rogue, achieves a stealth check of 22, easily beating an orc sentry's passive perception. She sneaks directly behind him and stabs him in the back. Surely the orc isn't surprised at all until the dagger hits him (or if Renee misses, she fumbles around behind him or something). What I think it really boils down to in the end is: when is initiative rolled? If (in our example) initiative is rolled before Renee's attack hits (or misses) how can we justify the orc recovering from his surprise before the action that triggered said surprise even occurs, should he roll better than Renee on his initiative? I'd like to go with initiative is rolled immediately following whatever event began the encounter (which could be an attack, but is likely to often be something else wherever surprise isn't intended), but I can't find any documentation to support this stance.  Why Does Anyone Care? There are many reasons you might want someone to be surprised while you're attacking - in this example if Renee is over L3 (and took the Assassin archetype) she'll get 'Assassinate' if the orc is surprised, and 'Death Strike' if she's over L17. That's a lot of potential extra damage!  that if the orc is surprised, Renee will be able to retreat and hide, without having to take the disengage action as her bonus action to avoid an attack of opportunity. Of course, there's no way for her to know whether the orc is surprised or not at that stage, so trying this would be a bit of a gamble... Considering the three types of Devil Fruits that has been explained are 1. Paramecia Type - where the user can get super human abilities and change their body parts into weapons, etc. 2. Zoan type - where the use can turn into a particular animal and inherit its abilities 3. Logia Type - where the user's body inherits a particular element and the body becomes like air which cannot be touched or damaged by non Haki users.  So what exactly is the type of Gomu Gomu no Mi? It cannot be Zoan or Logia. It's very close to a Paramecia but still doesn't have a logical explanation to be of Paramecia type! So is it some special type of Devil Fruit? Why do we use ./filename to execute a file in linux?  Why not just enter it like other commands gcc, ls etc... Is $\sqrt{x^2}=|x|$ or $=x$? Isn't $(x^2)^\frac12=x?$ $|x|=\sqrt{x^2}$ as  shows. But, as $(x^2)^\frac12=x$, I can't understand where am I wrong interpreting Square-root. What is currently the best way to get a favicon to display in all browsers that support Favicons? Lately it's happening to me this:  After completing one or more "First Posts" reviews, I go back to the Review Section main page:   And the post counter shows that there are still posts to review. I click the link to review them, but there is nothing.  Refreshing the page doesn't solve the issue: it shows the wrong number again. Why we don't use gamma rays, x-rays or ultraviolet to transmit data? When is matrix multiplication commutative? I know that matrix multiplication in general is not commutative. So, in general:  $A, B \in \mathbb{R}^{n \times n}: A \cdot B \neq B \cdot A$  But for some matrices, this equations holds, e.g. A = Identity or A = Null-matrix $\forall B \in \mathbb{R}^{n \times n}$.  I think I remember that a group of special matrices (was it $O(n)$, the ?) exist, for which matrix multiplication is commutative.  For which matrices $A, B \in \mathbb{R}^{n \times n}$ is $A\cdot B = B \cdot A$?