Show that f is not differentiable at (0,0)
Showing that a function is not differentiable
Tried to install both Windows and Ubuntu, now neither will boot FAQ for Stack Exchange sites Community FAQ For sites in the Stack Exchange 2.0 network To see a list of commonly used words and phrases, see the . For official guidance from Stack Exchange, visit the . Asking questions                            Answering questions                 Accepting answers        Working with posts  What does it mean when a question or answer is...  ?  ?  ?  ?                                       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Link back to this index. Paste this at the end of the question:  [Return to FAQ index](/q/7931)   Tag as  and .  When a post seems to have hit a mature state, it will have  added by a moderator.  Flag for a moderator to mark community wiki.  Any FAQ post not yet community wiki should be made into a community wiki.  After the post has the  tag added to it, add a link in the above . How to clear current “read-only” state on a USB flash drive I setup with Rufus? Three weeks ago I used  2.2 to install Windows 10 on my machine, and it has write-protected my flash drive. I’ve tried diskpart:  diskpart att disk clear readonly  clean create partition primary format fs=fat32 quick   And it kinda worked, it removed the image off the USB, but now it’s showing:  Current Read-only State : Yes Read-only  : No Boot Disk  : No Pagefile Disk  : No Hibernation File Disk  : No Crashdump Disk  : No Clustered Disk  : No   And I can’t format it or write on it.    The drive is a a Kingston DataTraveler G4 32GB model, without physical switches. How would I restore it back to normal (rw) state? Is there a way to give promo/coupon codes for people to download your app for free? How to Tail -f output with colors using only Awk and show the rest of the output? I was able to do a tail -f output with colors using the awk command. But I'm unsure how to output the rest of the log as it seems to be filtering only those 2 lines. I also want to see the other lines as the log is written.  What do I need to put in the awk command to show the rest of the output?  Image of my issue. The red text above is without using awk and displays the entire tail -f log. And below that is the same command with the awk color filtering. Turning off and on images in figures Is it possible to prevent the contents of a figure from being rendered? I have a large book document, and to speed up compiling while working on a draft, I would like to have some way of ignoring the content of the images, but ensuring that the figure size remains.  In several cases I am using a line like:  \includegraphics[width=\linewidth]{figure.pdf}     so I do not know the actual size of the image. finding rational roots of polynomials Could someone please explain me how to apply the Descartes's Criterion? For example , how do I find the rational roots of $ x^3 -x +1$.  I've been looking at some examples, but I get confused. We can say ‘fried fish’, ‘baked potato’ or ‘minced pork’ using past participles for modifiers.  However, ‘roast’ is different - either ‘roast duck’ or ‘roasted duck’ works, it seems to me.  How should we analyze this?  Is ‘roast’ a noun modifying a noun here, or is it a different form of the past participle?  (According to freedictionary.com, in Middle English the past participle was ‘roste’ – does that mean that this was once a strong verb?) How to fully backup non-rooted devices? Are Constitution changes retroactive when calculating max HP? Lets say I'm a fighter that just leveled up to level 4, and decide to bring my Constitution up from 16 to 18. How many hit points do I have?  Level 1 = 10 (base) + 3 (Con mod) = 13.  Level 2 = 10 + 6 (average HP per fighter level) + 3 (Con mod) x 2 = 22  Level 3 = 10 + 6 (average) x 2 + 3 (Con mod) x 3 = 31  Level 4 = 10 + 6 (avg) x 3 + 3 (Con mod) x 3 (3 level-ups) + 4 (increased Con mod, which is now 4) x 1 = 41?  OR  Level 4 = 10 + 6 (avg) x 3 + 4 x 4 (4 times current Con mod) = 44?  If it's the first option, it's simply better to level Constitution up at earlier levels. Let's say you have a few expressions like the following:  $$\begin{array}((x+17)^2 \\ x^2 + 34x + 289 \end{array} \\ 288 + \frac{x^2}{2} + \frac{x^2}{2} + 34x + 1 \\ [...] $$  You get the idea: there's an infinite number of ways of representing the same expression. The challenge is that my application is validating answers to math problems, input by math students practicing a certain concept. I'd like to make sure that whenever they submit an answer, the checker is completely insensitive to the issues of ordering, simplification, formatting etc. which would be plain frustrating. I'd also ideally like to support more than one variable such as x, y, z in the same expression.  What's a reliable way to check that two expressions are the same? The most brute force way I can think of would be to just plug a number into each variable of each expression and see what the result is.  I have a hunch however that there might be ways of getting false positives this way. That, and I might be either missing something really obvious about this, or there might be a better way of doing the comparison.  Would love to hear what you think. "All of the ...." or " All the ... "? SUB-TREE WITHIN A TREE in MySQL  In my MYSQL Database COMPANY, I have a Table: Employee with recursive association, an employee can be boss of other employee. A self relationship of kind (SuperVisor (1)- SuperVisee (∞) ).     Query to Create Table:    CREATE TABLE IF NOT EXISTS `Employee` (   `SSN` varchar(64) NOT NULL,   `Name` varchar(64) DEFAULT NULL,   `Designation` varchar(128) NOT NULL,   `MSSN` varchar(64) NOT NULL,    PRIMARY KEY (`SSN`),   CONSTRAINT `FK_Manager_Employee`                 FOREIGN KEY (`MSSN`) REFERENCES Employee(SSN) ) ENGINE=InnoDB DEFAULT CHARSET=latin1;   I have inserted a set of tuples (Query):    INSERT INTO Employee VALUES   ("1", "A", "OWNER",  "1"),     ("2", "B", "BOSS",   "1"), # Employees under OWNER   ("3", "F", "BOSS",   "1"),   ("4", "C", "BOSS",   "2"), # Employees under B  ("5", "H", "BOSS",   "2"),   ("6", "L", "WORKER", "2"),   ("7", "I", "BOSS",   "2"),   # Remaining Leaf nodes     ("8", "K", "WORKER", "3"), # Employee under F        ("9", "J", "WORKER", "7"), # Employee under I        ("10","G", "WORKER", "5"), # Employee under H   ("11","D", "WORKER", "4"), # Employee under C  ("12","E", "WORKER", "4")     The inserted rows has following Tree-Hierarchical-Relationship:                A     &lt;---ROOT-OWNER         /|\                     / A \               B     F      //| \    \              // |  \    K        / | |   \                       I  L H    C         /     |   / \  J     G  D   E   I written a query to find relationship:    SELECT  SUPERVISOR.name AS SuperVisor,          GROUP_CONCAT(SUPERVISEE.name  ORDER BY SUPERVISEE.name ) AS SuperVisee,          COUNT(*)   FROM Employee AS SUPERVISOR    INNER JOIN Employee SUPERVISEE ON  SUPERVISOR.SSN = SUPERVISEE.MSSN  GROUP BY SuperVisor;   And output is:    +------------+------------+----------+ | SuperVisor | SuperVisee | COUNT(*) | +------------+------------+----------+ | A          | A,B,F      |        3 | | B          | C,H,I,L    |        4 | | C          | D,E        |        2 | | F          | K          |        1 | | H          | G          |        1 | | I          | J          |        1 | +------------+------------+----------+ 6 rows in set (0.00 sec)   [QUESTION] Instead of complete Hierarchical Tree, I need a SUB-TREE from a point (selective) e.g.: If input argument is B then output should be as below...  +------------+------------+----------+ | SuperVisor | SuperVisee | COUNT(*) | +------------+------------+----------+ | B          | C,H,I,L    |        4 | | C          | D,E        |        2 | | H          | G          |        1 | | I          | J          |        1 | +------------+------------+----------+      Please help me on this. If not query, a stored-procedure can be helpful. I tried, but all efforts were useless! I am wanting to find a latitude and longitude point given a bearing, a distance, and a starting latitude and longitude.  This appears to be the opposite of this question ().  I have already looked into the haversine formula and think it's approximation of the world is probably close enough.  I am assuming that I need to solve the haversine formula for my unknown lat/long, is this correct? Are there any good websites that talk about this sort of thing? It seems like it would be common, but my googling has only turned up questions similar to the one above.  What I am really looking for is just a formula for this. I'd like to give it a starting lat/lng, a bearing, and a distance (miles or kilometers) and I would like to get out of it a lat/lng pair that represent where one would have ended up had they traveled along that route. Combining multiple textures with a white background I'd like to sort of "overlay" these shaders, but the only options are mix and add. Allow me to explain.  I made two images, both white background, one with red scribbles and one with blue scribbles, both 1920x1080. Image textures plugged into diffuse was my node setup. I want both scribbles to be added to the plane while the background stays the same color.  If I mix them I get the following:  The red and blue scribbles are now 50% dimmer than they would be on their own, and the white color hasn't changed in intensity.  If I add them I get the following:  The red and blue scribbles are still 50% dimmer than they normally would be (since the white background is being added over each). But the white background is now 2x brighter than normal.  Can I get a result where the white background is normal brightness and both the blue and red scribbles are at normal brightness? How do you configure email notifications in Cognito Forms? Software needed to scrape data from graph Anybody have any experience with software (preferably free, preferably open source) that will take an image of data plotted on cartesian coordinates (a standard, everyday plot) and extract the coordinates of the points plotted on the graph?  Essentially, this is a data-mining problem and a reverse data-visualization problem. Using regex inside if clause in bash Look at this if block:  #!/bin/bash  str="m.m" if [[ "${str}" =~ "m\.m" ]]; then     echo "matched" else     echo "not matched"     exit 1 fi  exit 0   This should print "matched", but it doesn't. Where am I going wrong? How do you solve a recurrence with a summation function inside: $t(n) = 1 + \sum\limits_{j=0}^{n-1} t(j)$ Show that  $$t(n) = 1 + \sum_{ j=0}^{n-1} t(j)$$  is the same as  $$t(n) = 2^n$$  Initial condition $t(0) = 1$ LLC-SCorp to self - actually, does the corp pay payroll taxes? In the USA. Here are the two common scenarios for the self-employed:  A. Joe makes 100,000 over the year. It's paid to him as 1099 payments from his various clients.  Joe pays the many taxes on that.  B. Joe makes 100,000 over the year.  He has an LLC as SCorp (or maybe an SCorp per se).  The clients pay $100,000 to the entity JoeCorp.  JoeCorp pays Joe a certain salary (it might be the whole 100,000, or, it might be (let's say) half of that and the rest is taken as profit distribution, not relevant here).  So, JoeCorp (his LLC) pays Joe say $50,000.  In fact: does JoeCorp have to pay "payroll taxes" on that??  Does it perhaps make a difference if it is an LLC with S-Corp election v. S-Corp?  (I realize there are many questions on here about "1099 v. corp" .... but I've never really understood this and can't seem to google it up.)