Integrate $\int \frac{(1+x^2)dx}{(1−x^2)\sqrt{1+x^4}}$
How do I integrate the following? $\int{\frac{(1+x^{2})\mathrm dx}{(1-x^{2})\sqrt{1+x^{4}}}}$
texstudio: show line numbers in editor How do I show line numbers in the editor? According to the picture in the doc (e.g. about bookmarks) there should appear by default.  I'm using Texstudio version 2.7, win8.1. How can I deactivate Bluetooth on system startup? In low-cost mass-produced items I often run into black blobs of what looks like resin applied directly on top of something on the PCB. What are these things exactly? I suspect this is some kind of custom IC that is layed out directly on the PCB to save on the plastic  housing/connector pins. Is this correct? If so, what is this technique called?    This is a photograph of the inside of a cheap digital multimeter. The black blob is the only non-basic piece of circuitry present, along with an op-amp (top) and a single bipolar junction transistor. Why don't electromagnetic waves require a medium? As I understand it, electromagnetic waves have two components which are the result of each other, i.e., when a moving electric charge creates a changing magnetic field at point X then a changing electric field is created at point Y and this repeating process is what creates EM waves, so therefore, it requires no medium. Is my understanding correct?  One thing that I'm surprised to know is that light is also called an electromagnetic wave.  Does this include light of any kind, for example: light from a bulb, a tube, and also from the Sun? How do they contain electric and magnetic fields? Exposing database IDs - security risk? I've heard that exposing database IDs (in URLs, for example) is a security risk, but I'm having trouble understanding why.  Any opinions or links on why it's a risk, or why it isn't?  EDIT: of course the access is scoped, e.g. if you can't see resource foo?id=123 you'll get an error page. Otherwise the URL itself should be secret.  EDIT: if the URL is secret, it will probably contain a generated token that has a limited lifetime, e.g. valid for 1 hour and can only be used once.  EDIT (months later): my current preferred practice for this is to use UUIDS for IDs and expose them. If I'm using sequential numbers (usually for performance on some DBs) as IDs I like generating a UUID token for each entry as an alternate key, and expose that. Why is logistic regression a linear classifier? Since we are using the logistic function to transform a linear combination of the input into a non-linear output, how can logistic regression be considered a linear classifier?  Linear regression is just like a neural network without the hidden layer, so why are neural networks considered non-linear classifiers and logistic regression is linear? 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? Propagate all arguments in a bash shell script How do I make the Unity Launcher background transparent? I found a way to make the icon backgrounds transparent for the Unity Launcher by changing the files under /usr/share/unity/4.  Does anyone know how to make the background transparent for the launcher itself? I already made it transparent under Compiz, but I want to remove the line that separates the launcher from the desktop. If anything, I just want to make it look like the icons are floating. Why was Edo Tensei Madara young, when he had died at an old age? From Naruto manga and anime, I know that Uchiha Madara died as an old person after he helped Uchiha Obito.   But it was bit weird for me, when Kabuto summoned Uchiha Madara-sama with Edo Tensei, Madara was a younger person.  Again, when Chiyo was summoned, she was older as when she died.  How can it be possible? I've got a development webserver on an Ubuntu box inside of VMWare Workstation 7.1.3. I'd like to run a web browser on a Windows machine (the host OS) for actually testing a web page I'm working on -- hard to run IE tests in Ubuntu :)  However, if I simply try to ping the IP given to the ubuntu VM (192.168.83.137) (or open it in my browser for that matter), it seems the host cannot communicate with the guest.  How do I allow the guest OS to communicate with the host when the guest is running in NAT mode? Error when updating texlive 2015 When I want to update packages of texlive 2015 I get this error? what is the problem?  tlmgr update --list  The locale codeset (cp720) isn't one that perl can decode, stopped at   C:\texlive \2015\tlpkg\tlperl\lib/Encode/Locale.pm line 123. Compilation  failed in require at C:\texlive\2015\tlpkg\tlperl\lib/LWP/UserAgent. pm  line 1001. Doppler redshift of distant galaxies gave first hint that the universe is expanding. I am curious to know how this redshift is actually measured and interpreted from observation. Suppose I observe some  visible line say red with wavelength \lambda_1.  This is not enough to tell that this line is redshifted, i.e., the  original line emitted from that galaxy had a smaller wavelength. How do I know the value of that particular line when it was emitted from that galaxy? It appears that mere observation of a line is not enough. So how do we proceed? Combining two expressions (Expression>) Many to Many and Weak Entities I have an entity that cannot exist without being defined by another, and I want this entity to participate in a many-to-many relationship.  Example: An artist has an album (the album cannot exist without an artist), the album also has many tracks, but the same track can exist in many albums.  So we have a many-to-many relationship between the album and the tracks.  If the album is a weak entity, then its primary key is a foreign key referencing the artist, thus it cannot be a foreign key to another table representing a many-to-many relationship.  The question is: is it possible to have this kind of relationship in SQL, and if so, how do I express it? I'm looking for a shapefile containing an 1000m or 2000m UTM grid ("graticule"). All I was about to find on the web is a 10000m UTM grid (here: ) and I am aware that a 1000m UTM grid for the whole world might be quite big.  That's why I'm now wondering if and how it would be possible to generate such a shapefile for a part of the world. I would prefer to use open source tools like gdal. Others output formats than a shapefile might be ok too.   Has anyone an idea? All nilpotent $2 \times 2$ matrices satisfy $A^{2}=0$ Assigning values to divergent series I have been looking at divergent series on wikipedia and other sources and it seems people give finite "values" to specific ones. I understand that these values sometimes reflect the algebraic properties of the series in question, but do not actually represent what the series converges to, which is infinity. Why is it usefull to assign values to divergent series?  The only theory I could come up with, is this:  Say you have 2 divergent series, series' A and B, and you assign each a value,   Series ($A= \sum_{n=0}^\infty a_n$), which I assigned the value Q  and series ($B= \sum_{n=0}^\infty b_n$ ), which I assigned the value P  But it just so happens that series $C=A-B= \sum_{n=0}^\infty (a_n-b_n)$ converges. Could that imply that the actual value of series $C$ is the difference of the two assigned values to $A$ and $B$, that is $\sum_{n=0}^\infty (a_n-b_n)=Q-P$ ?  If so, then that would make some sense to me, as to why people sometimes assign values to divergent series. Sometimes it’s possible to use either a noun adjunct or the possessive case.     the shop door   the shop’s door   However, in certain phrases it’s not OK to do so.     the ship’s crew (the ship crew is wrong)   The questions are:   How can one find out what to use in such cases as “the shop(’s) door” when a noun adjunct option and the possessive case option are available?  How can one know which option is wrong in order to avoid the construction “ship crew”? Is there a difference in meaning between (a) the shop door (b) the shop’s door? How to remove Apple System Apps How can I delete Apple OS X application such as Photos, iPhoto, and others that I never use?