Using the (!!!) operator in JavaScript?
What does the '!!!' syntax mean in javascript?
A great Python IDE for Ubuntu Possible Duplicate:          I want to develop Python apps in Ubuntu, and I'm tired of working with gedit one time and another.  So I'm trying to find a great Python IDE (a true IDE, not just a syntax-highlighting editor) on the Ubuntu repositories. Which one do you recommend me? I have installed VirtualBox OSE on Ubuntu 11.04 and Windows XP pro as the virtual machine. Now I want to have a shared folder which can be accessed on both, my host Ubuntu machine, and my WinXP guest virtual machine.  How can I do that? Proving a relation between inradius ,circumradius and exradii in a triangle Prove that in a triangle $$r^2+r_1^2+r_2^2+r_3^2=16R^2-(a^2+b^2+c^2)$$ where the symbols have their usual meanings. I am looking for a smaller or elegant proof using trigonometry. A geometric proof would be super cool. I did prove it but it took me ages to do the calculation. Thanks. Preview Breaks with Invalid Tag Name [tag:+] In the formatted preview for Questions &amp; Answers, typing a tag link with an invalid tag name "crashes" the preview. As soon as you type the following the preview stops updating and an error can be observed in the Javascript console.   [tag:+]   Observed in Safari 7 and Chrome 31.   seems related to the business rule of not allowing certain characters in tags, but it sounds like a different bug. "All the good people" vs. "all of the good people" Can you construct a field with 4 elements? Can you construct a field with 4 elements? can you help me think of any examples? What are the differences between vector graphics and raster graphics? $$(1+2+\cdots+n)^2=1^3+2^3+\cdots+n^3$$  I noticed this only because $\displaystyle \sum_{i=1}^n i = \frac{n(n+1)}{2}$ and $\displaystyle \sum_{i=1}^n i^3 = \frac{n^2(n+1)^2}{4}$.  But the two things look completely different and I can't think of an intuitive reason I would have seen this connection. Something like the 'Proof Without Words' images. Or a trick I could use while expanding the right hand side to transform it to the sum of cubes. Does mass distribution/center of mass affect free fall? An everyday is example would be cars. If you were to drop a car, not taking air resistance into account, would a front-heavy car tumble forward as it fell? And a car with a perfect 50/50 front/rear weight distribution fall straight? Does mass distribution/center of mass affect free fall? Or would they both fall straight down without tumbling? Can you explain why please? How to allow to run su instantly after I added the user to the appropriate group I have the su executable with the following permissions:  bash-4.2# ls -la /bin/su -rws--s--- 1 root wheel 59930 Sep 14  2012 ./su   When I am logged in as a user, not in the wheel group and try to run su, I get an error, which is correct:  bash-4.2$ su bash: /bin/su: Permission denied   After that I add this user to wheel group from root:  bash-4.2# usermod -a -G wheel user   But for the same terminal session I still can't run su:  bash-4.2$ su bash: /bin/su: Permission denied   For the new sessions I can run su. How to allow to run su instantly after I added the user to the appropriate group? How come unpolarized light does not undergo destructive interference? As far as I know, unpolarized light is defined as light which has no clear axis of polarization, but electric field vectors in all directions. However, I also know that electric fields can be superpositioned. So this leads me to the conclusion that if unpolarized light has equal $\vec E$ vectors in all directions, they should cancel.   Obviously, though, this is wrong (we've got light!). What's the explanation? Beamer Tikz-cd Problem Using Integration By Parts results in 0 = 1 How exactly does Knuth's Up-Arrow notation work? in my mariadb i have replication, i tried to change the location of the binlogs by changing the configuration file as so: log-bin = /new/path/mysql-bin I also tried to change the index location as so: log_bin_index = /new/path/mysql-bin.index but every time when I restart I see that the location of the binlog files is /var/lib/mysql... i tried to check with mysqld --verbos --help | grep bin and I saw that the lob-bin parameter is mysql-bin and not what I wrote in the cnf... how to I make the MySQL to take the value of the log-bin from the cnf file? this is the cnf file of the MySQL for sure... I recently bought myself a pack of four YN560 IV's and a YN560-TX for my Canon camera, and apparently I got ahead of myself and didn't realise I should make sure the flashes support HSS.  I tried them out yesterday at home, and even on 1/128 and 1/250s on the camera, they were overexposing here and there. Unfortunately, I don't really have the space to move the flashes much further from my subject, so I was wondering if there is any way to trick them into HSS? I should mention that I also own a Canon 580ex II, which does support HSS. I was thinking I could perhaps use that mounted on the camera to trigger the Yongnuo's, but as far as I can tell that would render the 560-TX useless as the flashes can't be controlled wirelessly when in S1 or S2.  I guess I could buy an ND filter, but as I have lenses with differing sizes, this feels like more of a pain in the ass.  Is there any hack I can pull off here that you guys know of?  Thanks! Evaluate the limit: $$\mathop {\lim }\limits_{x \to \infty } x\left( {{{\left( {1 + {1 \over x}} \right)}^x} - e} \right)$$  My attempts didn't yield a result. I'd be glad for a guidance. Thanks! How to install pip for python 3 in ubuntu 12.04 LTS What is the difference between sector and cluster? I have gone through wikipedia and other sites and here's the information I have obtained.  Sector: Smallest Addressable Unit (mostly 512 bytes) Cluster: Smallest Allocation Unit (equals to 1 or more sectors and the number of clusters depends on the file system).  Let's say in the below example:  sector =512 bytes and a cluster =8 sectors=4096 bytes. Now, I am having a hard time figuring out, when I am trying to create a file what does the file system do? Does it consider 4096 bytes as the smallest write/read unit or 512 bytes?  If the answer is 4096 bytes: When the manufacturer of the disk drives has provided 512 bytes as the smallest addressable unit, why does the file system consider cluster as the smallest unit? I mean, what are the advantages in doing so? Let $G$ be a finite abelian group, then $G$ has a subgroup of order $n$ if and only if $n\mid G$.  Proof: by Lagrange if $H\leq G$ then $|H|$ divides $|G|$ so this proves one of the implications.  We prove the other implication by strong induction on the order of $G$, for primes this is just Cauchy, so we can take these like base cases. Now let $n$ be a proper divisor of $|G|$, take $p$ a prime in the factorization of $|G|$ (instead of $|G|$ is should be $n$, I had made a mistake when typing the first time), then by cauchy there is an element $x$ of $G$ of order $p$, since $G$ is abelian $\langle x\rangle$ is normal in $G$ so we can look at the quotient group $G/\langle x\rangle$, this group has order $\frac{|G|}{p}$, now take a prime $p_1$ in the factorization of $\frac{|G|}{n}$. By induction the quotient group has a subgroup $E$ of order $G/pp_1$ now look at the preimage of $E$ under the natural homomorphism from $G$ to $G/\langle x\rangle$, it is easy to see this is a subgroup of $G$, we call it $I$, consider the restriction of the natural projection to $I$, this is a surjective homomorphism from $I$ to $E$ with kernel $\langle x\rangle$ so by the first isomorphism theorem $I/x\cong E$ so $\frac{|I|}{|\langle  x\rangle|}=|E|\implies  |I|=\frac{|G|}{pp_1}{p}=\frac{|G|}{p_1}$ Notice $\frac{|G|}{p_1}$ is a multiple of $n$ since $p_1$ was in the fatorization of $\frac{|G|}{n}$. So by induction $I$ has a subgroup of order $n$ which is also a subgroup of $G$.