Vector subtraction proof
Prove that $||x|-|y||\le |x-y|$
What is the value of $p^2q + q^2r + r^2p$ for the given cubic equation? If p,q,r are the real roots of the equation $x^3-6x^2+3x+1=0$ then find the value of $p^2q + q^2r + r^2p$?  My Attempt: I tried $(p+q+r)(pq+qr+rp)$ but couldn't really figure out what to do with the extra terms. The roots are also not trivial to find. Any help would be appreciated. Integer squares of the form $x^4+x^3+x^2+x+1$ I want to solve ${y^2}=x^4+x^3+x^2+x+1$ in $\mathbb{Z}$.    I can find four solutions. Is there another solution? I know that there are six solutions. $$(-1, \pm 1)\;,\;(0, \pm 1).$$  My try: \begin{align}   &amp; x^4+x^3+x^2+x+1=0\quad \Rightarrow \underbrace{\left( x+\frac{1}{x} \right)^2}_{t^2}+\underbrace{\left( x+\frac{1}{x} \right)}_{t}-1=0\,\Rightarrow t\notin \mathbb{Z} \\   &amp; x^4+x^3+x^2+x+1={\pm 1}^2\quad\Rightarrow \,x=-1\,\,,\,x=0.\\  \end{align}   Thanks. Prove that if $a^2 = a$ for all elements of the ring $R$, then $R$ has characteristic 2. Is the converse of the statement true?  Attempt:  by the definition of characteristic of a ring, the first statement implies that characteristic of the ring is $\leq 2$. If the ring is assumed to be non trivial ring then, characteristic is 2.  About the last statement can we construct a field of say 8 elements and show that there exists a an element of order $\neq 2$?  Is there a simpler example ? What is XLNC an example of? XS sounds like excess, B4 sounds like before, XLNC sounds like excellency, etc.  What are these wordplays called? Is there a way to display a player name in /tellraw command? like the title says, I'm looking for a way to display a player name in a /tellraw command which is run by a command block. Example:  /tellraw @a {"text":"","extra":[{"text":"A player has won the game!","color":"blue"}]}   And the output is something like this:  A player has won the game!   But I want the output to be something like  JasonSPQR has won the game!   Using the @p parameter How can I remove the site URL from enqueued scripts and styles? I'm dealing with an SSL issue and I would like to strip the domain from all scripts and styles being output via wp_enqueue_scripts. This would result in all scripts and styles being displayed with a relative path from the domain root.  I imagine there is a hook that I can use to fileter this, however, I am not sure which one, nor how to go about it. How to make 7-zip do a whole bunch of folders Are there any differences between URLs with and without "www" and "http://" Are there any differences among these addresses?     www.example.com http://www.example.com example.com Obligatory: This is not a duplicate of , which is concerning the much older duplicate closure process.  Have a gander at . Notice anything weird?  The Community♦ user was invoked by the question asker to self-close as a duplicate (presumably of the comment below, which links to ), but the list of duplicates is entirely empty. So it would seem the question asker was able to close their own question as a duplicate of... nothing?  Screenshot, in case the post is altered later:    Any idea what happened here? Floor function properties: $[2x] = [x] + [ x + \frac12 ]$ and $[nx] = \sum_{k = 0}^{n - 1} [ x + \frac{k}{n} ] $ I'm doing some exercises on Apostol's calculus, on the floor function. Now, he doesn't give an explicit definition of $[x]$, so I'm going with this one:     DEFINITION Given  $x\in \Bbb R$, the integer part of $x$ is the unique $z\in \Bbb Z$ such that $$z\leq x &lt; z+1$$ and we denote it by $[x]$.   Now he asks to prove some basic things about it, such as: if $n\in \Bbb Z$, then $[x+n]=[x]+n$  So I proved it like this: Let $z=[x+n]$ and $z'=[x]$. Then we have that  $$z\leq x+n&lt;z+1$$  $$z'\leq x&lt;z'+1$$  Then $$z'+n\leq x+n&lt;z'+n+1$$  But since $z'$ is an integer, so is $z'+n$. Since $z$ is unique, it must be that $z'+n=z$.  However, this doesn't seem to get me anywhere to prove that  $$\left[ {2x} \right] = \left[ x \right] + \left[ {x + \frac{1}{2}} \right]$$  in and in general that   $$\left[ {nx} \right] = \sum\limits_{k = 0}^{n - 1} {\left[ {x + \frac{k}{n}} \right]} $$  Obviously one could do an informal proof thinking about "the carries", but that's not the idea, let alone how tedious it would be. Maybe there is some easier or clearer characterization of $[x]$ in terms of $x$ to work this out.  Another property is $$[-x]=\begin{cases}-[x]\text{ ; if }x\in \Bbb Z \cr-[x]-1 \text{ ; otherwise}\end{cases}$$  I argue: if $x\in\Bbb Z$, it is clear $[x]=x$. Then $-[x]=-x$, and $-[x]\in \Bbb Z$ so $[-[x]]=-[x]=[-x]$. For the other, I guess one could say:  $$n \leqslant x &lt; n + 1 \Rightarrow  - n - 1 &lt; x \leqslant -n$$  and since $x$ is not an integer, this should be the same as $$ - n - 1 \leqslant -x &lt; -n$$  $$ - n - 1 \leqslant -x &lt; (-n-1)+1$$  So $[-x]=-[x]-1$ Make a computer act as a virtual USB device for other equipments List all files in all subfolders Find remainder of division of $x^3$ by $x^2-x+1$ I am stuck at my exam practice here.      The remainder of the division of $x^3$ by $x^2-x+1$ is ..... and that of $x^{2007}$ by $x^2-x+1$ is .....   I tried the polynomial remainder theorem but I am not sure if I did it correctly.  By factor theorem definition, provided by ,     the remainder of the division of a polynomial $f(x)$ by a linear polynomial  $x-r$ is equal to $f(r)$.   So I attempted to find $r$ by factorizing $x^2-x+1$ first but I got the complex form $x=\frac{1\pm\sqrt{3}i}{2}=r$.   $f(r)$ is then $(\frac{1+\sqrt{3}i}{2})^3$ or $(\frac{1-\sqrt{3}i}{2})^3$ which do not sound right.  However, the answer key provided is $-1$ for the first question and also $-1$ for the second one. Please help. Let $M,N$ be $n \times n$ square matrices over an algebraically closed field with the properties that the trace of both matrices coincides along with all powers of the matrix. More specifically, suppose that $\mathrm{Tr}(M^k) = \mathrm{Tr}(N^k)$ for all $1\leq k \leq n$. The following questions about eigenvalues is then natural and I was thinking it would be an application of Cayley-Hamilton but I am having trouble writing out a proof.  How do we show that $M$ and $N$ have the same eigenvalues?  Added (because this question is now target of many duplicates, it should state its hypotheses properly). Assume that all the mentioned values of $k$ are nonzero in the field considered; in other words either the field is of characteristic $0$, or else its prime characteristic $p$ satisfies $p&gt;n$. How do I create a line graph which ignores zero values? I want to create a graph showing trends over time, calculated from a formula of various data.  However, some data is missing, resulting in zeroes in the calculated data which the chart uses.  When plotting this data against as a line graph, it's drawing a line down to the axis, which I don't want.  I'd like either a gap in the line, or skip the data point and draw from directly previous to next.  i.e. given this data:  00.0    61.6    39.5    74.6    86.8    72.0    66.5    99.5    85.6    80.6    95.0    122.4 81.0    83.1    88.2    00.0    94.3    60.5    00.0    99.5    95.8    86.2    00.0    111.4 84.1    110.8   78.9    62.0    75.9    102.2   89.9    87.1    81.6    73.5    00.0    116.9   All the 00.0 items mean "no data", so I'd like them ignored (not treated as 0 value).   This is the chart I currently have:   This is how I'd like the chart to come out:   Again, I don't mind if the dotted lines are blank or solid, so long as they don't go down to zero.  The data is dynamic/calculated, so I can't just say =AVERAGE(prev,next) since I don't know where missing data will occur in advance - I need a solution which takes this into account.  Any ideas? How can I download a distribution? Am I right in thinking that the Drupal distributions that I can download from  are a standard Drupal core download with a load of other stuff added at /profiles?  Anyone know if there are any plans to create a dev branch of distributions that would automatically update the core version that the distribution is running on? Currently it seems that the distribution runs on whatever core version its developer has chosen.  And how can I use distributions with Drush? Is there an equivalent to drush dl drupal that will download a specific distribution?  And, finally, is there any difference between an install profile and a distribution? Is $L^{p}$ space with alternate norm Banach? How long does the new dwellers queue last? When clicking the radio room icon that attracts a new dweller to your vault, how long will they stay queued out in front of the vault for before giving up?  Or will they?  I'm at max population and would rather not kill existing dwellers to accommodate them in my vault. Group $G$ of order $p^2$: $\;G\cong \mathbb Z_{p^2}$ or $G\cong \mathbb Z_p \times \mathbb Z_p$ If the order of $G$ is $p^2$ then how do I show that $G$ is isomorphic to $\mathbb Z_{p^2}$ or $\mathbb Z_p\times\mathbb Z_p$. 1.  Why is the wave function complex? I've collected some layman explanations but they are incomplete and unsatisfactory. However in the book by Merzbacher in the initial few pages he provides an explanation that I need some help with: that the de Broglie wavelength and the wavelength of an elastic wave do not show similar properties under a Galilean transformation. He basically says that both are equivalent under a gauge transform and also, separately by Lorentz transforms. This, accompanied with the observation that $\psi$ is not observable, so there is no "reason for it being real". Can someone give me an intuitive prelude by what is a gauge transform and why does it give the same result as a Lorentz tranformation in a non-relativistic setting? And eventually how in this "grand scheme" the complex nature of the wave function becomes evident.. in a way that a dummy like me can understand.  2.   A wavefunction can be thought of as a scalar field (has a scalar value in every point ($r,t$) given by $\psi:\mathbb{R^3}\times \mathbb{R}\rightarrow \mathbb{C}$ and also as a ray in Hilbert space (a vector). How are these two perspectives the same (this is possibly something elementary that I am missing out, or getting confused by definitions and terminology, if that is the case I am desperate for help ;)   3.   One way I have thought about the above question is that the wave function can be equivalently written in $\psi:\mathbb{R^3}\times \mathbb{R}\rightarrow \mathbb{R}^2 $ i.e, Since a wave function is complex, the Schroedinger equation could in principle be written equivalently as coupled differential equations in two real functions which staisfy the Cauchy-Riemann conditions. ie, if $$\psi(x,t) = u(x,t) + i v(x,t)$$ and $u_x=v_t$ ; $u_t = -v_x$ and we get $$\hbar \partial_t u  = -\frac{\hbar^2}{2m} \partial_x^2v + V v$$ $$\hbar \partial_t v  = \frac{\hbar^2}{2m} \partial_x^2u - V u$$ (..in 1-D) If this is correct what are the interpretations of the $u,v$.. and why isn't it useful. (I am assuming that physical problems always have an analytic $\psi(r,t)$).