How to install a CA key (self signed SSL) on ubuntu?
How do you add a certificate authority (CA) to Ubuntu?
What the #$@&%*! is that called? Every time I click to open a link, other windows start opening. They all want to sell me Detox your Mac or have warnings about how my Mac is at risk or infected.  How can I check for malware? R's lmer cheat sheet FireFox 66 Quantum disabled all my extensions at midnight! This morning I woke up to:    and the FireFox help page doesn't really help...  Help!  What should I do now??? I need NoScript and AdBlock Plus to improve my surfing speed!!! 0:-) Add a non-breaking space to "reopen (1)" and its ilk Relation between real roots of a polynomial and real roots of its derivative I have this question which popped in my mind while solving questions of maxima and minima. First Case:Let $f(x)$ be an $n$ degree polynomial which has $r$ real roots. Using this can we say anything about the number of real roots of $f'(x)$?  Second Case:Suppose, $f(x)$ has all  $n$ real roots. Then will all of its derivatives also have all real roots?  Also, if any of its derivatives do not have all real roots, then will $f(x)$ also have not all real roots? If the above is true then what about its converse?  Comment Case:For the third case:Suppose f'(x) is a 5 degree polynomial with 3 real roots.Then f(x) will be a 6 degree polynomial.(correct me if I am wrong).What are the possible no. of roots that f(x) can have(3,4,5 etc.?).Basically I am asking for an example.Also it would be great if you follow all cases with an example like in the 4th case. Books for a beginner I am a student of 11th grade and i have completed the syallabus of both 11th and 12th grade maths with complete understanding and it was possible coz of the love for this subject that i have. I don't want to sound "larger than life" here, but my curiousity has now increased to learn maths at a deeper level. As of now i am reading "Linear algebra done right" by Axler. Thats an amazing piece of work and now i truly understand what "matrix" is all about. I also want to extend my knowledge on the following topics :  1) Algebra (groups,subgroups,homomorphisms etc)   2) Analysis   3) Geometry/Topology  Why i am here is because i wanted you guys to recommend a book on each of the above topic that would be appropriate for a beginner like me (I must mention here I have been working on Apostol's volume 1 calculus, thats a great text, but for a beginner, its best if the concept is explained in a broad manner and in as simple and easy words as possible) . I just want a book which explains the concept broadly rather than coming to the conclusion directly (which is not a great sight for a beginner like me) .   Having said that, no book is complete i understand. Thats why i am asking your recommendation as you guys are aware which text would be the best to start with for a beginner. I have searched on the net about this, but there are dozens of works available, and out of them all , i want the one which is the best (approximation) for a beginner .   Please don't misunderstand me in any way. I am just confused which text to go for, and i understand the books which u may suggest may be for undergraduate level course as these topics are for undergraduate level courses, thats not a problem at all . I need a easy to learn (i mean easy in terms of "broad" explanation) book. I hope you guys don't mind me questioning such a question on this forum . Thanks for all the help you guys have been providing me on this forum . Maths Maths Maths... the world is beautiful coz of u! :)) Solving a Second Order Constant Matrix Differential Equation Given that $A$ is a constant coefficient matrix, how would one find a non-zero solution to the following equation: $$ x''+2Ax'+A^2x=0 $$ I am thinking this could incorporate systems of linear equations, but I am not sure how to use $x'=Ax$ or $x'=P(t)x +g(t)$ in this situation.   Any hints or suggestions are appreciated. Is it safe to cancel CHKDSK when it has been started without any parameters? I know that it is not a good idea to forcibly stop a chkdsk process that has been executed with parameters like /f and /r.   But is it safe to stop the process when it has been started simply by the chkdskcommand? Chkdsk prints out a lot of errors and is continuing very slowly.  I suppose it to should be safe to cancel the process since there should be only in read mode, correct? Close vote review audit is broken - displays "on hold" while reviewing I just reviewed this:    But while reviewing, it already displays the "put on hold as not a real question" section, and it asked:     Should this question be closed as: ?   So as it stands, the audits are broken, since we already know that the question is "on hold" while reviewing, and it is incredibly hard to miss the huge grey box at the bottom.  Another with screenshot: Covering estate tax on US assets for non-resident alien I am a non-resident alien holding a brokerage account in the USA but residing outside the USA. My country does not have an estate tax treaty with the USA. So my estate is liable for a significant estate tax up to 40%. Is there any way to avoid or to cover this tax? I thought of buying term insurance for myself, but I am not sure whether US companies will sell term insurance to a non-resident. I want to buy insurance from a US company because I want the death benefit to be in USD. Can someone suggest as to what the best way to approach this issue is? What can I do to increase passive HF RFID read range? I am working on a prototype, one function of which is to detect whether an object is "in range" by a few cm. Right now I'm just using an Arduino and a cheap  that operates at 13.56 MHz:    I've successfully gotten it to detect the tag, but only at a distance of about 3-4 cm when the tag is oriented parallel to the antenna.  According to my  , the HF band allows read ranges of between 10 cm and 1 m for passive tags, depending on factors like antenna size, tag size and orientation, and transceiver power.  I realize this inexpensive reader is not up to task as-is, but I'm interested in building something that achieves read ranges of 15-20 cm.  Some criteria:   No need to read multiple tags; only whether one tag is in range or not. No need to write to the tag. Cannot use an active tag.   I'm not experienced with RFID reader construction (yet) but am interested in knowing what I should pursue.  Here are some things I've considered:   Ditch the embedded antenna on the cheap RFID reader and construct my own, larger antenna. I'd need to see if the onboard  is up to the task of providing additional power. Look for a different IC around which to build a reader from scratch. Find a ready-made solution instead of trying to build one (more cost-effective?). Use something other than RFID for simple proximity detection.   I am experienced with microcontrollers and basic electronics, and have made audio and lighting projects, but this is a first with RFID. Since I don't need to read multiple tags, which RFID is suitable for, I've considered maybe some sort of magnet and hall-effect sensor, but the range does not seem adequate. I considered using an ultrasonic proximity detector, but the application calls for detecting the tagged object while ignoring untagged ones (ultrasonic would produce false positives on untagged objects). I've considered some sort of reflective surface placed on the object, and detecting reflected light, but the object orientation is not reliable enough to maintain alignment.  So, in a nutshell, What modifications can I make to my existing reader, or what alternate technology should I pursue to achieve 15-20 cm detection of a passively tagged object?  I plan on connecting whatever proximity detector is used to a microcontroller using SPI. Is it ethical to use a recommendation letter from a deceased professor? She was a really nice professor and she wrote me a good recommendation letter that resulted in a lot of good results with applications. Recently, this professor died from brain cancer, which was a fast and shocking death for me.  Tomorrow is the deadline for a grant. What should I do? Is it professional to use letters from the deceased? If $d(x,y)$ is a metric, then $\frac{d(x,y)}{1 + d(x,y)}$ is also a metric Let $(X,d)$ be a metric space and for $x,y \in X$ define $$d_b(x,y) = \dfrac{d(x,y)}{1 + d(x,y)}$$ a) show that $d_b$ is a metric on $X$  Hint: consider the derivative of $f(t)$ = $\dfrac{t}{1+t}$  b) show that $ d$ and $ d_b $ are equivalent metrics. c) let $(X,d) $ be $(\mathbb{R}, |\cdot|)$ Show that there exists no $ M&gt;0$ such that $ |x-y| $ $\leq$ $Md_b$ $(x,y)$ for all $ x,y$ $\in$ $\mathbb{R}$  I have calculated $f(t)$ and $f'(t)$ and from this I know $f(t)$ is an increasing function as $f'(t)$ is strictly positive. But I don't know where to go from here or how to do parts b) and c) Volumes of n-balls: what is so special about n=5? The volume of an $n$-dimensional ball of radius $1$ is given by the classical formula $$V_n=\frac{\pi^{n/2}}{\Gamma(n/2+1)}.$$  For small values of $n$, we have $$V_1=2\qquad$$ $$V_2\approx 3.14$$ $$V_3\approx 4.18$$ $$V_4\approx 4.93$$ $$V_5\approx 5.26$$  $$V_6\approx 5.16$$ $$V_7\approx 4.72$$ It is not difficult to prove that $V_n$ assumes its maximal value when $n=5$.   Question. Is there any non-analytic (i.e. geometric, probabilistic, combinatorial...) demonstration of this fact? What is so special about $n=5$? I also have a similar question concerning the $n$-dimensional volume $S_n$ ("surface area") of a unit $n$-sphere. Why is the maximum of $S_n$ attained at $n=7$ from a geometric point of view?   note: the question has also been  for those curious to other answers. How can I animate the Restrict Visibility property of an object? I've been trying to create an animation where an object blinks on and off.   For example, I have a Cube and I set a keyframe on it's Restrict Visibility icon (the "eye" icon) with I, then I toggle off that "eye" so my cube doesn't show in the Viewport and again I press I to record that keyframe. Then, when I preview the animation in the Viewport, I see my cube appears and then disappears like I want, but when I render it, the cube does not disappear at all.  What am I doing wrong? What was the meaning of the Night King's message? In S08E01 of Game of Thrones, we see this message:    We have seen this several times, the symbol drawn with horse heads, the stones around the Weirwood where White Walkers are created and in some caves, drawn by Children of the Forest.  Do we know the meaning behind this symbol? Does it or something similar occur in the books as well? Is it possible to exclude questions I've already answered from the search criteria? Recently I asked if it were possible to find questions with just one answer and as a result we got an .  That's great, but ...     Is there a way to restrict the search to questions where that one answer isn't mine? That would help. :-)   It's certainly possible to search for , but it's not possible to exclude your own posts as far as I can tell:   -user:me searches for posts that . user:1-67 doesn't search for posts from user #1 to user #67, but searches for .  (And I'm not sure that will help anyway since I don't think it would be possible to simultaneously exclude 69-max(userID).) -Ericson searches for posts that , but since my last name is in the the metadata and not the searchable portion of posts: no joy.   And of course none of this will actually work to eliminate the questions that that I've answered already and want to ignore.  In general, If I'm involved in a Q&amp;A (or ) the notification procedures do a good job of keeping me up-to-date with developments.  But when I search, it's often to find questions I've not noticed before.  So being able to eliminate questions I have already answered would be a generally useful feature for me. What is the difference between a symbolic link and a hard link? Recently I was asked this during a job interview. I was honest and said I knew how a symbolic link behaves and how to create one, but do not understand the use of a hard link and how it differs from a symbolic one. Tikz and ctable incompatibility, gives error when printing When I print a report I get an error:     An error exists on this page. Acrobat may not display the page   correctly. Please contact the person who created the PDF document to correct the problem   After a lot of debugging, I've found that this MWE reproduces the problem. I've tried it on three different computers with the same error.   \documentclass{standalone}           \usepackage{tikz} \usepackage{ctable} \begin{document} \begin{tikzpicture} \filldraw[opacity=.5] (0,0) rectangle (1,1); \end{tikzpicture} \end{document}   When loading the ctable package, the image is changed (the opacity disappears), so it seems the error comes from some incompatibility between ctable and opacity in tikz. The error only appears when trying to print though, acrobat before attempting to print. (Printing either to a pdf file or to a real printer)  I have the following versions of tikz and ctable:      tikz.sty    2013/12/13 v3.0.0   ctable.sty    2014/04/25 v1.29   How can I fix this?    EDIT: I found the warning Transparency disabled: incompatible with tikz package from ctable so I guess this incompatibility can explain the error in the first MWE.  However, I continued digging and found that the spy library seem to be incompatible with ctable as well.   Here's an MWE that generates the same error when printing (either to a pdf file or to a real printer):   \documentclass{standalone}           \usepackage{tikz} \usetikzlibrary{spy} \usepackage{ctable} \begin{document} \begin{tikzpicture}[spy using outlines={size=2cm,connect spies}] \begin{scope} \spy on (-3,.25) in node at (2,0); \end{scope} \end{tikzpicture} \end{document}   There seem to be a serious problem with using tikz + ctable, can it be fixed?