I think that it has something to do with Brewster's Angle, but not really sure
Why do polarized sunglasses remove (most) reflections on car windows?  I know that both lenses of polarized sunglasses are polarized in the same direction and I can see that reflections in my own windshield and the windows of other cars appear, disappear, or change depending on how I tilt my head, but why?  Why is the light in those reflections polarized?  edit: And why is most of the light in the various reflections on the interior of my own windshield and various windows/windshields at what seem like a variety of angles all polarized in a sufficiently narrow set of ways as to make polarized sunglasses work?
What is the purpose of delayed suspend (Ctrl-Y) in Bash? Finding the limit $\lim \limits_{n \to \infty}\ (\cos \frac x 2 \cdot\cos \frac x 4\cdot \cos \frac x 8\cdots \cos \frac x {2^n}) $ How can I find the difference between two angles? Uniform convergence of $\sum\limits_{k=1}^{\infty}\dfrac{kf(x^2)}{1+k^3f(x^2)^2}$ Cu has an unpaired electron in 4s, but it is diamagnetic. I thought that it has to be paramagnetic. What am I missing? What does the dot mean At what times before $1{:}30$ in the afternoon do all three doctors schedule their appointments to begin at the same time? In a certain medical group, Dr. Schwartz schedules appointments to begin $30$ minutes apart, Dr. Ramirez schedules appointments to begin $25$ minutes apart, and Dr. Wu schedules appointments to begin $50$ minutes apart. All three doctors schedule their first appointments to begin at $8{:}00$ in the morning, which are followed by their successive appointments throughout the day without breaks. Other than at $8{:}00$ in the morning, at what times before $1{:}30$ in the afternoon do all three doctors schedule their appointments to begin at the same time?  I'm not sure how to approach this question. They all begin at the same time at $8{:}00$. Also doesn't the overlapping of appointments depend on how long their respective appointments take? translation invariant of integral on $\mathbb{R}$ Problem 1: Let $f\in L^1(\mathbb{R})$, show $\int_\mathbb{R}f(t)dt=\int_{\mathbb{R}}f(x+t)dt,\forall x\in (-\infty, \infty)$.  Problem 2: Let $f\in L^1(\mathbb{R})$,show $\displaystyle \lim_{t\rightarrow 0}\int_{\mathbb{R}}|f(x+t)-f(x)|dx=0$.  My try for Problem 1:  Consider $\displaystyle \int_{\mathbb{R}}f(t)dt=\lim_{n\rightarrow \infty}\int_{-n}^nf(t)dt=\lim_{n\rightarrow \infty}\int_{\mathbb{R}}f_n(t)dt$, where $f_n(t)=f(t)\chi_{[-n,n]}$.  And since $dt=d(x+t)$, we have $\displaystyle \int_{-n}^nf(x+t)dt=\int_{-n+x}^{n+x}f(t)dt$.  So for each $x\in (-\infty,\infty)$,  $$ \begin{split} \int_{\mathbb{R}}f(t)-f(t+x)dt &amp;=\lim_{n\rightarrow \infty}\int_{\mathbb{R}}f(t)(\chi_{[-n,n]}-\chi_{[-n+x,n+x]})dt\\ &amp;=\lim_{n\rightarrow \infty}\int_{\mathbb{R}}f(t)(\chi_{[-n,-n+x]}-\chi_{[n,n+x]})dt\\ &amp;=\lim_{n\rightarrow \infty}\lim_{k\rightarrow \infty}\int_\mathbb{R}\varphi_k(t)(\chi_{[-n,-n+x]}-\chi_{[n,n+x]})dt\\ &amp;=\lim_{k\rightarrow \infty}\lim_{n\rightarrow \infty}\int_\mathbb{R}\varphi_k(t)(\chi_{[-n,-n+x]}-\chi_{[n,n+x]})dt \end{split} $$ where $\varphi_k(t)$ is simple function pointwise converges to $f(t)$, simple function vanish out of set of finite measure, so $\varphi_k(t)(\chi_{[-n,-n+x]}-\chi_{[n,n+x]})$ vanishes when $n$ big enough(is this right?)    Another try:  Since $f\in L^1$, $f$ is bounder a.e. so can be approximated by simple functions, and $\chi_{A+t}(x)=\chi_A(x-t)$,thus $$\int f(t)=\lim_n\int\varphi_n=\lim_n \sum_{i=1}^nc_i\mu(E_i)=\lim_n \sum_{i=1}^nc_i\mu(E_i-x)=\int f(t+x)$$  For problem 2, I guess they share the same method.   Any help or correction about these two problems? Thanks. What is the standard interpretation of the order of operations for an expression involving some combination of grouping symbols, exponentiation, radicals, multiplication, division, addition, and subtraction? SEDE logs me out more often than it used to do I'm pretty sure that since a month or so,  seems much more eager to get rid of my session and log me out in that process. I don't mind logging in a couple of times per day, if that helps to reduce resource consumption, but the user experience isn't all that great when it happens. Here is why: I'm most often in the middle of writing a query for an MSE question, for example . So I have the edit window open and am creating a new revision of my query. When I click &quot;run,&quot; I do notice the button gets grayed-out, as it normally does, but I never get any result back. There is also no error message. To recover from this I have to copy the SQL text I have typed, open a new tab and load SEDE, log in, switch back to the stalled tab, refresh, paste the SQL text, run query. Repeat the process after 10 minutes. If the intended behavior is to log users out of their session on such short notice (I recall sessions lived for 24 hours), can there then be a slightly better handling in the browser of that state, so it is clear you're logged out once you click the run button? I prefer, however, to have the longer allowed sessions back. I'm experiencing this behavior mostly in Chrome on Win 10. Why are the moderators being so strict with quality related flags recently? The following quote from  assumes "the URL" comes from somewhere and uses it to restrict the Host header. Where does "the URL" come from? Is it from the first line of a HTTP request (e.g. after GET), or from the input to a web client (e.g. an argument to curl, or the input in the address bar of a web browser)? Thanks.     The Host header specifies the Internet host and port number for the   resource being requested, as obtained from the original URL:  Host = "Host" ":" host [ ":" port ]       In particular:      • If the Host header does not contain a port, the default port for the   scheme is assumed.      • If the URL contains an IP address, the Host header should contain   the same address.      • If the URL contains a hostname, the Host header must contain the   same name.      • If the URL contains a hostname, the Host header should not contain   the IP address equivalent to the URL’s hostname, because this will   break virtually hosted servers, which layer multiple virtual sites   over a single IP address.      • If the URL contains a hostname, the Host header should not contain   another alias for this hostname, because this also will break   virtually hosted servers. I use Firefox 35.0 on my Macbook to access Stack Exchange. Recently whenever I access a message or Community site, the "spinning circle" indicating activity starts, and never stops. This doesn't seem to happen on other non-Stack Exchange sites.  Has there been any change to the SE code which may have caused this.    The Web Developer Console shows  The connection to ws://qa.sockets.stackexchange.com/ was interrupted while the page was loading. full.en.js:1 Use of getPreventDefault() is deprecated.  Use defaultPrevented instead. jquery.min.js:3 How to add existing user to an existing group? I want to add the Apache user (www-data) to the audio group. I've read the man page for useradd, but I'm not having any luck. I'm running xubuntu 11.10. Here's what I'm doing:  $ sudo useradd -G audio www-data useradd: user 'www-data' already exists   If I leave out the -G option, bash, prints the help info for useradd:  $ sudo useradd  audio www-data Usage: useradd [options] LOGIN Options: -b, --base-dir BASE_DIR       base directory for the home directory...   It's not clear to me from the man page what options I should use to make this work. Conditional Expectaction 3 variables Suppose $X,Y$ and $Z$ are multivariate normal with means and full covariance matrix. The conditional expectation $E(X | Y)$ is well know. What is the conditional expectation of $E(X | Y,Z)$ if $Y$ and $Z$ (and $X$) are correlated? Standard textbooks only seem to cover the case when $Y$ and $Z$ are uncorrelated. No option to create a new Managed Path inside Office 365 SharePoint online 2013 I am working on an Office 365 SharePoint online 2013. Now when I wanted to create a new private site collection, inside the online SharePoint admin center, I did not find the option to create new managed path, as I use to get when creating a site collection inside SharePoint on-premise. So how do I create a new managed paths inside SharePoint online? How can I synchronize my two Mac Computers? natbib: combining chicago style and sorting by appearance How can I deduce/identify an app from a notification icon? I'm concerned about an app on my child's phone. I saw an app icon in the notification area that looked strange (Andy Android head, slightly tilted as its icon).  How can I find out what app it is from just having seen that icon in the notification bar? Can wizards really cast spells in armor?