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8:08 PM
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Q: Geometry (using vectors or complex numbers) problem involving points on a triangle and on a circle

Sudipto BanerjeeLet ATS be a fixed acute-angled triangle, i.e., all the three angles of the triangle are less than 90 degrees. Let E and F be two points on the sides AS and AT, respectively, such that the segment EF is parallel to the segment TS. Let M be the midpoint of EF and let MN be the perpendicular bisect...

Title contains problem.
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Q: how do I find the inverse function of x = ky - cos(y) where k is a constant

Olivier de BroquevilleIn other words, I'd like to express y in terms of x instead of having x expressed in terms of y! I just don't know how to proceed!

Short question.
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Q: Evaluate using logs

Abmon98Evaluate lim k-->infinity (1+1/k)^k Is there another approach to this solution other than l'hoptital. Here's my working till now ln(1+1/k)^k=kln(1+1/k) As k-->infinity ln(1+1/k)-->0 due to the fact that ln(1)=0

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Q: Growth of Ramsey Numbers

Mike HartAt what rate do Ramsey Numbers grow? Please include a proof of this for k colors.

Short question.
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Q: please help me :(

user290084prove that if 2a+5b is multiple of 7, then 5a+2b is also multiple of 7.

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Q: Injectiv, bijectiv

Alena EverdeenCan someone check if this is good? y=-10x^5 is injective y=10|x| is surjectiv e^(4x) is bijectiv for A = R B = N C = [0, infinite) E = (-pi/2, pi/2) F = (-1,1) J = (-10,10)

Welcome to Math.SE, user290084. Words such as please, help do not add information to titles. Please edit the title so that it better describes the specifics of your question. Do not hesitate to make it longer or include a formula if needed. More tips at: How to ask a good question? (autocomment)Normal Human 29 secs ago
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Q: A baisc question about dual space

hahaHow to show that the dual space of $R^n$ with Taxicab norm is $R^n$ with sup norm? Thanks!

Words such as question do not add information to titles. Please edit the title so that it better describes the specifics of your question. Do not hesitate to make it longer or include a formula if needed. More tips at: How to ask a good question? (autocomment)Normal Human 25 secs ago
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Q: If the $X_i$'s are IID, are the $X_i^2$'s IID as well?

David SouthIf we have a sequence of random variables $X_1, X_2, \cdots$ of IID random variables, is the sequence of random variables $X_1^2, X_2^2, \cdots$ also a sequence of IID RVs?

Short question.
 
8:55 PM
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Q: How do I solve log_3(x) = 4log_x(3)

MatthewI am currently revising for my Additional Maths test and cannot figure out a way to get the solutions for the following questions. I know I have to use the change of base rule, but when I try it doesn't work. a) log_3(x) = 4log_x(3) b) log_2(x) - 4 = 5log_x(2) c) 2log_4(x) + 3log_x(4) = 7 I hav...

Welcome to Math.SE, Matthew. This site uses MathJax formatting of formulas. More tips at: How to ask a good question? (autocomment)Normal Human 25 secs ago
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Q: sketch the region of triple integral and express it in the five other possible orders

user286826Sketch the region of the triple integral $$\int_{0}^1 \int_{0}^{y} \int_0^{x} x^2yz dzdxdy$$

Short question.
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Q: SemAntics predicate logic

Davidφ is valid if and only if for every structure A, A 􏰀 φ. We write this as 􏰀 φ. Definition: φ is satisfiable if and only if there is a variable assignment s such that s satisfies φ, i.e., A 􏰀 φ[s]. Prove that if 􏰀 φ, then ∼φ is not satisfiable

Welcome to Math.SE, David. Consider adding a tag for a broader subject area to which the question belongs. Some of these tags might fit. (autocomment)Normal Human 25 secs ago
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Q: How do you calculate the wife's age?

user290097A computer engineer is twice as old as his wife was when he was as old as his wife is now. He is 24. How old is his wife?

Short question.
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Q: I need help factoring 6q(7(6q)^2 +5)

JohannStraussCan someone please show me how to factor 6q(7$(6q)^2 +5) to show that it is a multiple of 6? I'm working on a division algorithm problem, and I understand concepts of div alg but I really don't have much experience factoring and I can't find any good sources on learning this type of thing. Thank ...

Words such as help do not add information to titles. Please edit the title so that it better describes the specifics of your question. Do not hesitate to make it longer or include a formula if needed. More tips at: How to ask a good question? (autocomment)Normal Human 23 secs ago
 
9:13 PM
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Q: Point Googlers to new Q&A and redirect them away from outdated Q&A

LynobI think that SO answers are usually better than blog posts, but some questions should stop appearing in google. A lot in PHP or any language has changed. Things we considered good back then, now considered bad, things considered secure, now easy to crack. I suggest two things: If a new questio...

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Q: What to do with potentially dangerous answers?

Paranoid PandaI was just wondering, what should one do with potentially dangerous answers? I mean I have read before on Meta that I should just flag them up, however when I did so for this one I just got this: declined - flags should not be used to indicate technical inaccuracies, or an altogether wrong answe...

 
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Q: Rotating a cone from z-axis to x-axis

Ryan AdLet say I have a cone located on z-axis. I have this equation: (x^2+y^2)/r^2=(z-z0)^2/h^2 I made a matlab code to make this figure, but I want it pointing to Z plane. here is the image: (http://i.imgur.com/RBD2r7y.png?1) I cannot rotate it on matlab, so I think I have to modify the equation. ...

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Q: Find the double roots of the quadratic equation

user290098(M-1)x^2+2(m+3)x+(m-7)=0 Please find the double roots of this equation . Please solve!!

Short question.
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Q: Probability Question regarding the counting principle

KingJahksA parking lot contains 100 cars, k of which happen to be lemons. We select m of these cars at random and take them for a test drive. Find the probability that n of the cars tested turn out to be lemons. Here is a picture of my work I understand what the sample space of the question is (100 choo...

Welcome to Math.SE, KingJahks. Words such as question do not add information to titles. Please edit the title so that it better describes the specifics of your question. Do not hesitate to make it longer or include a formula if needed. More tips at: How to ask a good question? (autocomment)Normal Human 44 secs ago
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Q: linear modeling question: How can I find variance for vector Y?

B11bLinear models are $$Y_1= 2\theta_1+3\theta_2 +\epsilon_1$$ $$Y_2= -2\theta_1+\theta_2 +\epsilon_2$$ and $\epsilon_1=3z_1-z_2$ and $\epsilon_2=4z_1+z_2$, where $z_1, z_2$ are two random variance such that its independent mean is 0 and variance is $\sigma^2$ I have written this model as $Y=X\be...

Please don't use (self-learning) tag just because you were self-studying. This tag is only for questions about the process of self-studying. (autocomment)Normal Human 40 secs ago
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Q: Basic proofs for epsilon delta limits

QualityHello I am wondering if my approach and understanding of the epsilon delta definition is correct. For example, if I wanted to use it to show that $$\lim_{x \to c} \frac{x}{1+x}=\frac{a}{1+a}$$ for $a \in \mathbb{R}, a \neq -1$ Then here are my thoughts; I know that we want that for all $\epsil...

Title contains basic. Tagged proof-verification.
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Q: Where am I going wrong when trying to prove $\lim _{ x\rightarrow \infty }{ \frac { 1-2x }{ 3-4x } =\frac { 1 }{ 2 } } $

Cherry_Developer$$\lim _{ x\rightarrow \infty }{ \frac { 1-2x }{ 3-4x } =\frac { 1 }{ 2 } } $$ Proof: Let $\epsilon > 0$ Then, $$\left| \frac { 1-2x }{ 3-4x } -\frac { 1 }{ 2 } \right| <\epsilon$$ $$\Longleftrightarrow \left| \frac { 2-4x }{ 6-8x } -\frac { 3-4x }{ 6-8x } \right| <\epsilon $$ $$\Longleft...

Title contains wrong.
 
9:49 PM
-2
Q: What's dim V at this problem?

Hamed Baghal GhaffariLet $A$ be a $2\times 2$ matrix which is diagonalizable and $V=\{B\in M_{2\times 2}\mid AB=BA\}$. What's the $dim V$?

Title contains problem. Short question.
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Q: what's wrong with this code

DreamerI am trying to test if the given number N is a power of 2: public class Solution { public boolean isPowerOfTwo(int n) { if(n ==1) return true; if(n%2 != 0) return false; if(n%2 ==0) { isPowerOfTwo(n/2); } return true ; } }

Title contains wrong.
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Q: Negative Mean Square Error

B11bFor simple random sampling, I have calculated somemean square errors for ratio-type estimators such as Isaki estimator, and Prasad Singh estimator. But, Mean Square Errors i obtained are negative. Does MSE eqaul to a negative value? I there a mistake ?

Please don't use (self-learning) tag just because you were self-studying. This tag is only for questions about the process of self-studying. (autocomment)Normal Human 22 secs ago
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Q: Let A be a non-empty set and $f:\emptyset \rightarrow A$, why f must be 1-1?

Andi ZhangLet A be a non-empty set and $f:\emptyset \rightarrow A$, why f must be 1-1 ? This is a part of my Sets Numbers and Functions' mid-term test, I'm still confusing about it...

Short question.
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Q: Let A be an n x n matrix. Col(A^2)=R^n if and only if Col(A)=R^n

DrearieeHow would I go about proving the following statement? "Let A be an $n x n$ matrix. $Col(A^2)=R^n$ if and only if $Col(A)=R^n$" I started off by proving that A is linearly independent if and only if $Ax=0$ which implies that $x=0$. I showed that the columns of A span $R^n$ if and only if Ax=b ha...

Tagged proof-writing.
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Q: How to write the SDP in cvx for the following optimization problem

tourismHow to write the SDP(Semidefinete program) of the following optimization problem \begin{multline} \max_{Z,f ,g} \ trace(KZ) − f^Td \\ subject to \\ trace(W^{−1}Z) = k \\ Z_{ij} ≥ 0 \\ Z = Z^T \\ Ze = Wf \\ e^Tf = (1 + α)n \\ e^T g ≥ (1 − β)n \\ f \geq g \\ 0 \leq g \leq 1 \end{multline} I have ...

Title contains problem.
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Q: Uncorrelated and X given Y = 0

bluepinkIs the following true or false: Suppose that X and Y are two discrete random variables defined on the same probability space. If E[X] = E[Y] = 0 and E[X | Y=y] = 0 for all y∈S Y, then X and Y are uncorrelated. How does this tell me E[XY] = 0?

Title contains 0.
 
10:05 PM
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Q: Why isn't CS functioning as MathExchange or StackOverflow?

portalI understand that all the forums serve different purposes, and they have their own moderators, rules and policies. But CS seems completely different to me, with respect to all the other forums I have used. The most significant difference that surprised me is that one will never get a solution. I...

 
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Q: Let A be an n × n matrix and let P be an n × n invertible matrix. Prove that det($P −1$AP) = det(A)

BNSlugPretty lost on this one, partially because I don't understand the relationship between the determinant of a matrix and the determinant of its inverse. Thanks.

Short question.
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Q: Is there a problem of plane geometry whose analytic reformulation gives a polynomial non-solvable by radicals?

Sébastien PalcouxThis answer explains that any elementary plane geometry problem can be reduced to the existence of a solution of a polynomial system (called the analytic reformulation). Question: Is there a problem of elementary plane geometry whose analytic reformulation gives a polynomial non-solvable by ra...

Title contains problem.
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Q: How to perform Cellular Edge Detection Algorithm?

brkI am trying to perform a cellular edge detection algorithm. The pseudo-code of this algorithm : The CED algorithm The probablity vector for the learning automaton to be updated : where a and b are the reward and penalty parameters. Also, the local rule for CLA is : Bi,j=F(N)= 1 if Ai,j =A(N) ...

Questions tend to get more attention when they have a tag for a broad area of mathematics relevant to the question. Some of these tags might fit. (autocomment)Normal Human 21 secs ago
Short question.
 
10:39 PM
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Q: What do I do if I hate maths but can't avoid it?

Georgina DavenportThis isn't strictly a maths question but it is a questions about maths. Should it be in meta? I don't know. I have a deep problem in that I had not expected how deep my disliking for mathematics goes. I do genuinely detest the subject with a passion. Sadly, it's also a crucial part of my degree...

Tag (advice) should not be the only tag a question has. Please add a tag for a subject area to which the question belongs. (autocomment)Normal Human 21 secs ago
 
10:50 PM
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Q: $G$ is a group, if ∀a,b∈G, $a^2b=ba^2$, is $G$ Abelian?

user290115$G$ is a group, if ∀a,b∈G, $a^2b=ba^2$, how to make a counterexample show that $G$ is NOT Abelian? What's the counterexample when $a^nb=ba^n$?

Short question.
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Q: Conditional expectation on two variables to conditional expectation in 1 variable

confusedstudentI am really confused trying to prove the following statement formally although it makes perfect intuitive sense. I want to show that if $Y$ is conditionally independent on $W$ given $X$, then: $E[W|X]=E[W|X,Y]$ I know I have to use the Law of Iterated expectations but I am failing to see how ...

Welcome to Math.SE, confusedstudent. Questions tend to get more attention when they have a tag for a broad area of mathematics relevant to the question. Some of these tags might fit. (autocomment)Normal Human 20 secs ago
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Q: Let V be a vector space, and T:V→V a linear transformation

beginningprogrammersuch that T(5v⃗1+3v⃗2)=−5v⃗ 1+5v⃗ 2 and T(3v⃗ 1+2v⃗ 2)=−5v⃗ 1+2v⃗ 2. Then T(V1) = 5V1 + 4V2 T(V2) = ?V1 + -5V2 T(4V1 - 4V2) = ?V1 + ?V2 Can someone give me a hand on how to solve these problems, I would appreciate it. Thank you.

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Q: How do you calculate 3BC?

blakeeatsZenUrgently need help on this! Let's say I have 2 matrices, both 2x2, B = [2,6,8,16] and C = [6,12,24,1] How would I calculate the matrix for 3BC?

Short question.
 
11:09 PM
-3
Q: Gave bounty to wrong answer - reversing bounty?

stack1I made a mistake and gave a bounty to another answer instead of the one I selected as best answer. How do I take back the bounty and give it to the correct answer ? Link - How do I extract rows from a PDF file into a csv file?

 
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Q: Inverse Laplace for Large Equation

Green_XeoActually, I do not have mathematica. Currently I tried to use another famous software to obtain inverse Laplace for below equation. Unfortunately, the software is unable to do it. So, I am wandering if Mathematica can do it. If Mathematica do, I will join you. Obtain the inverse laplace for bel...

Welcome to Math.SE, Green_Xeo. This site uses MathJax formatting of formulas. More tips at: How to ask a good question? (autocomment)Normal Human 21 secs ago
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Q: Help with permutation question

Jonhy HubeettoHow many ways are there of seating six people at a round table so that two specific people sit together? I think it is a permuation question but not 100% sure. Thanks

Welcome to Math.SE, Jonhy Hubeetto. Words such as help, question do not add information to titles. Please edit the title so that it better describes the specifics of your question. Do not hesitate to make it longer or include a formula if needed. More tips at: How to ask a good question? (autocomment)Normal Human 20 secs ago
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Q: Find k such that the following matrix M is singular.

lukasM= 4 -4 2 -8 7 -6 -30+k 22 -16 I keep getting -6 but its marked incorrect Thanks

Short question.
 
11:37 PM
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Q: Please help explain a proof in Durrett's book: stochastic calculus.

TonyThis is from the book stochastic calculus: a practical introduction. I don't understand the last sentence in the picture. Could anyone help explain why the first one is a local martingale? Thanks so much!

Title contains please, help.
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Q: Find the limit of these two problems using l'hopital's rule

MichaelI could use some help solving these 2 problems. I've finished the rest, I just need help on these two. I know I'm supposed to use natural log and l'hopitals rule. As the limit goes to 0, find tan(x)^sin(x). As the limit goes to infinity, find (e^x+x)^1/x I tried to use natural log for both o...

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Q: Palindrome arrangement problem

Jonhy HubeettoHow many five-letter palindromes are there (using ordinary 26 letter alphabet)? I was thinking it was either using permutation with first three leters or using 26 cubed. Thanks

Title contains problem.
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Q: Handle a Radical Containing a Binomial

Argent DrakeI have the following problem : pretty version sqrt(x+8) - sqrt(x-4) = -2 So far my thinking is to isolate sqrt(x+8) by changing our equation to -2 + sqrt(x-4) = sqrt(x+8) When we square all of it, i'm running into my issue. I don't understand what I should be doing with my binomial left over. A...

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Q: Find the minimal polynomial for the given matrix.

RagingBullThe first part is trivial. How to go about the second part?

Short question.
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Q: Get local coords from global coords

QuleryI need to get local coords from global coords. I did not find ready-made examples. OPEN IMAGE Please help me how to do it on the example image. Thank you!

Short question.
 
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