0
votes
1answer
24 views

Trace evaluation via complex analysis

We are given $U$, $V$ unitary matrices of size $N \times N$ whose spectral decomposition is known (in my specific problem, $N=4$, and $U$, $V$ are matrices with real coefficients but we can keep it ...
1
vote
2answers
48 views

proof of number of prime factors of $n$

Given an integer $n$ between 1 and 1000000, how do you directly prove that $n$ has at most 19 prime factors (with multiplicity)? I'm quite stuck on how to do this. I can understand the base case ...
0
votes
0answers
6 views

On the hyperboloid model, if the point $\mathbf{v}$ gets translated to the origin, then where does the point $\mathbf{x}$ go?

Wikipedia has the answer in the case of the Poincaré disk model. When the point $\mathbf{v}$ is translated to the origin, then the point $\mathbf{x}$ is translated to $$\frac{(1 + 2\mathbf{v} \cdot ...
1
vote
2answers
50 views

Historical Approach to $\lim_{x \to 0} \frac{e^{\alpha x} - e^{\beta x}}{x}$, without L'Hospital's Rule

I encountered this problem, amongst others, in the slightly older Calculus textbook Piskunov's Differential and Integral Calculus when I was working with a student: Calculate the limit $$ \lim_{x \to ...
1
vote
2answers
81 views

Convergence in distribution for $\frac{Y}{\sqrt{\lambda}}$

Given a sequence of independent r.v's $\{X_n\}_{n\geq 1}$ such that $P(X_n=x)=\frac{1}{2}$ if $x=-1$ and/or $x=1$ Let $N\in Po(\lambda)$ be independent of $\{X_n\}_{n\geq 1}$ and we set that ...
0
votes
5answers
60 views

Deriving Euler's theorem from Fermat's little theorem

I would like to know why $a^p \equiv a \pmod p$ is the same as $a^{p-1} \equiv 1 \pmod p$, and also how Fermat's little theorem can be used to derive Euler's theorem, or vice versa. Please keep in ...
1
vote
2answers
18 views

Evaluating the bounds for a triple integral

I've working on the problem: Evaluate $\iiint_Q$ $1/(x^2 + y^2 + z^2)$, where Q is the solid region ABOVE the xy-plane (and we must do this in spherical coordinates). What I've done thus far is ...
2
votes
1answer
25 views

How do you evaluate elements of the Drinfeld double $D(H)$ against elements of $H^\ast$ or $H$?

Proposition 8.2 of Majid's primer on quantum groups says that if $H$ is a finite dimensional Hopf algebra with quantum double $D(H)$, then this is a factorizable Hopf algebra with quasi-triangular ...
4
votes
1answer
45 views

troubles showing existence of Clifford-algebra

We had the following definition in class: Let $V$ be a vector space, $K$ a field and $Q$ be a quadratic form. We call $(C(V,Q),j)=C$ a Clifford-algebra if: $C$ is an assoziative algebra with 1, ...
-3
votes
0answers
32 views

Minimal polynomial for primitive root

Let $p(x)$ be a polynomial over $Q[x]$. Prove that if $p(x)$ has as root a 5th primitive root of unity, then all 5th primitive roots are roots of $p(x)$ This would mean $p(x)$ is a multiple of $f(x) ...
2
votes
2answers
17 views

A balloon rises at a certain rate (in body), What is velocity of balloon after 40 seconds?

A balloon rises vertically from the ground so that its height after $t$ seconds is $h(t) =\frac12t^2+\frac12t$ feet where $t$ is between $0$ and $60$. What is the velocity of the balloon after $40$ ...
1
vote
1answer
11 views

Is it possible to make a linear reformulation?

The question is what to do when we have a product of the three variables, quite different in their nature. One is binary, the second is real, and the third is from a discrete set of rational numbers. ...
4
votes
0answers
50 views

Name of $|x|^p+|y|^p\le (|x|+|y|)^p$ ($p\ge 1$)?

I checked these What is the difference between square of sum and sum of square? Prove $(|x| + |y|)^p \le |x|^p + |y|^p$ for $x,y \in \mathbb R$ and $p \in (0,1]$. It is easy to see $p$-th power ...
1
vote
3answers
53 views

Gender Birth problem - Conditional probability

A family has two children. Assume that birth month is independent of gender, with boys and girls equally likely and all months equally likely, and assume that the elder child’s characteristics ...
0
votes
1answer
401 views

How to find the limits of integration to get the area for a loop of a lemniscate?

I know how to integrate the squared radius to get the equation that'll give me the area, like such for a lemniscate with $r^2=8\sin(2\theta)$ : $$1/2\int 8sin(2\theta) = 4 \int \sin(2\theta) = 4 * ...
1
vote
1answer
48 views

Number of Automorphisms of a Irregular Graph.

I have been looking for results on number of graph automorphisms of irregular graph(upper and lower bound). I searched , but could not find anything which can be used directly. Say, $G$ is $k$ ...
5
votes
1answer
77 views

How to get to the heart of a subject?

(mathematical subject is intended) It's obviously not a simple question, but I thought it could lead to some interesting discussion. I was reading Lewis Campbell's biography of James Clerk Maxwell ...
1
vote
2answers
44 views

Limit of Fraction

$$\lim_{x \to \infty} \frac{(1 + x)^{x/(1 + x)}\cos^{4}x}{e^{x}}$$ Attempt: I've tried evaluating the limits of the terms individually using the property of limits. Also, $y=1/x$ subsituition hasn't ...
2
votes
1answer
25 views

Field norm of $F(\sqrt[n]{a})$

Let $F$ be a field of characteristic zero that contains a primitive $n^{th}$ root of unity. Pick $a$ such that $K=F(\sqrt[n]{a})$ is a cyclic extension of $F$ of degree $n$. Let $\sigma$ be a ...
0
votes
0answers
18 views

Hieroglyphic from Herschel to Babbage?

John Herschel sent a letter to Charles Babbage in which he included this hieroglyphic with the message "Interpret it, it contains a great discovery". Personally I have no clue what it could mean. ...
2
votes
2answers
972 views

Every $k$ vertices in an $k$ - connected graph are contained in a cycle.

Let $G$ be a $k$-connected graph. Meaning, $G$ has no less than $k$ vertices, and for every set of $k-1$ or less vertices, if we remove them from $G$, the graph stays connected (Of course, $G$ itself ...
3
votes
1answer
45 views

Find probability of a Poisson process.

Given that $N=\{N(t)\mid t\geq 0\}$ is a Poisson process with parameter $\lambda>0$ I need to find $P(N(3)=2\mid N(1)=0, N(5)=4)$ So this is a conditional probability (can anyone clarify if this ...
0
votes
0answers
15 views

Proof verification regarding asymptotics

Prove $f(z)=o(\phi (z))$ implies $f(z)=O(\phi (z))$ as $ z \to 0$. My proof is: The assumed statement is $$\lim_{z \to 0} \frac{ f(z)}{\phi (z)}=0$$ That statement implies the function $\frac{ ...
1
vote
2answers
21 views

Find supremum and infimumm of a set with two variables

$$A= \left\{\frac{m}{n}+\frac{4n}{m}:m,n\in\mathbb{N}\right\}$$ Since $m,n\in \mathbb{N}$, infimum is zero because $m,n$ both are increasing to infinity. Then the supremum is $5$ when $m,n$ are ...
2
votes
3answers
99 views

How can I try myself to solve exponential equations easily?

I spent hours try to solve: $$4^x + 1 = 2^{x+1}$$ Can you guide me on how to solve this? How can I train myself to always find the right "trick" to solve such equations? Rather than just ...
0
votes
1answer
29 views

Problem of Conditional Probability

I am learning Probability from Sheldon Ross book. One of the problems starts by giving the probability $P_N$ that there are no matches when $N$ people select from among their own $N$ hats as ...
3
votes
1answer
37 views

Some questions about an exercise about $C^\infty \subset L^\infty$

Let $$ L^\infty (\mathbb R) = \{f : \mathbb R \to \mathbb C\mid \text{essential sup of } f < \infty \text{ and } f \text{ Borel measurable} \}$$ and $$ C^\infty (\mathbb R ) = \{ f: \mathbb R ...
-3
votes
0answers
214 views

polynomial cohomology

Hope this finds you all well. I want to make sure of one thing : Do we usually have polynomial cohomology only in case the cohomology modules are free of rank 1 at most in each degree? PS:I don't ...
1
vote
2answers
29k views

Calculate width and height of a rectangle, given its diagonal and ratio

Well, I know, it's easy. We did it in class some time ago and I forgot it, I'm stupid because I can't figure it out: E.g. I have a 32" TV with 16:9 ratio and I want to know its width and height. I'd ...
1
vote
1answer
71 views

How to rigorously establish this limit of sums

Assuming that $$\lim_{n}\sum_{k\geq 0} f\left(\frac{k}{\sqrt{n}}\right)g_n (k)=\int_{\mathbb{R}} f(u)g(u)\mathsf du,$$ (where $f$ is $C^2$ and $g$ and $g_n$ are probability distribution functions) I ...
2
votes
4answers
50 views

Vector Subspace

I have a question regarding vector subspaces: show $U=\{A\in M_{22} \mid A^2=A\}$ is not a subspace of $M_{22}$. I have said: let $A={(a_1, a_2, a_3, a_4) = \begin{pmatrix} a_1 & a_2 \\ a_3 & ...
0
votes
0answers
10 views

Binary solutions of multivariate polynomial system in special (factored) form.

In my personal research I've run into a system of multivariate polynomials (with coefficients in a field). I am aware that there is no polynomial time algorithm (in the number of indeterminates) for ...
1
vote
1answer
396 views

Classify relations “is greater than or equal to”

Classify the following relations as reflexive, irreflexive, symmetric, antisymmetric or transitive. Explain each property in the context of the question. “is greater than or equal to” on the set of ...
2
votes
2answers
38 views

Distance of two hyperbolic lines

Consider the upper-half plane model of the hyperbolic plane $\mathbb {H}^2.$ Now consider two lines in it given as $\ell_1:=\lbrace { (x, y)\in \mathbb {H}^2 \vert x^2 +y^2=r^2\rbrace}, ...
4
votes
2answers
37 views

External bisectors of the angles of ABC triangle form a triangle $A_1B_1C_1$ and so on

If the external bisectors of the angles of the triangle ABC form a triangle $A_1B_1C_1$,if the external bisectors of the angles of the triangle $A_1B_1C_1$ form a triangle $A_2B_2C_2$,and so on,show ...
-3
votes
0answers
17 views

How to show that the following preradical is left exact? [on hold]

Let $\widetilde { \sigma }$ be the preradical defined by the equation $\widetilde { \sigma }(M)=\sigma(EM)\cap M$ for each $M\in R$-Mod ($EM$ denotes the injective hull of $M$). Show that it is left ...
0
votes
2answers
8 views

Statistical Dependency Transitivity

I came across this question here on Stack Exchange, and it didn't address something that I then became curious about. If $X_1, X_2$ are dependent and $X_2, X_3$ are dependent, then are $X_1, X_3$ ...
6
votes
0answers
185 views

Does the set of $m \in Max(ord_n(k))$ for every $n$ without primitive roots contain a pair of primes $p_1+p_2=n$?

I have made the following observation: for those n even numbers that do not have primitive roots modulo n ,$Pr(n)$, the set $M(n)$ of those $k$ having a maximum multiplicative order $ord_n(k)$ ...
0
votes
1answer
26 views

Line segment equation in polar coordinates

I have a line segment given by two points $A$ and $B$. $$A+u(B-A), u\in[0,1]$$ when doing calculations with this segment, it would be advantageous to have it written in polar coordinates around some ...
0
votes
0answers
6 views

How do you prove that every AF C*-algebra is finite?

A C*-algebra $A$ is finite if $s^*s=1$ implies $ss^*=1$. A C*-algebra $A$ is AF if: for all $a_1,\ldots,a_n\in A$ and $\varepsilon>0$, there exists a finite-dimensional C*-subalgebra $B_n$ of $A$ ...
7
votes
1answer
933 views

Why the Riemann hypothesis doesn't imply Goldbach?

I'm interested in number theory, and everyone seems to be saying that "It's all about the Riemann hypothesis (RH)". I started to agree with this, but my question is: Why then doesn't RH imply the ...
1
vote
1answer
43 views

Prove that for a group with even order $2k$, there is a subgroup $K$ with order $k$

I'm trying to understand the proof my teacher did: Consider a subgroup $H$ of $G$. If $H$ is not contained in $A_n$, then we can say that there exists at least one permutation in $H$ that is odd ...
2
votes
0answers
144 views

Find third geographic coordinate in triangle using spherical earth model

I'm trying to solve triangulation problems using geographic coordinates from a GPS. all calculations must use the spherical earth model (great circle distance). Given the points and lengths: Point ...
4
votes
1answer
568 views

Determining partial derivatives and cross products for bicubic interpolation using function values only?

I'm trying to implement a bicubic interpolation algorithm. In order to calculate the interpolated values, I need to calculate sixteen coefficients used in the calculation process - and that's where ...
7
votes
2answers
198 views

Show that the series $\sum\left(\exp\left(\frac{(-1)^n}{n}\right)-1\right)$converges, but not absolutely.

Show that the series converges, but not absolutely. $\sum_{n=1}^{\infty}( $exp$(\frac{(-1)^n}{n})-1)$. My Try: Let $a_n=$exp$(\frac{(-1)^n}{n})-1$. I was going to use alternating series test ...
1
vote
1answer
25 views

Partition of a group such that an operation can be defined

I'm struggling with Problem 43 of 3.1 of Dummit's algebra book. The problem is: Assume $P=\{A_i\}$ is any partition of $G$ with the property that a "quotient operation" is defined as follows: to ...
0
votes
0answers
10 views

Possible to eliminate mutual information between random variables by reducing the number of them?

Say you have a set of random variables that have some mutual information structure. Could be that they all have nonzero MI between them. Or perhaps there are some clusters of variables with ...
3
votes
0answers
29 views

How to find unkown height of triangle without hyptenuse

I been trying to solve this question and have tried to solve it for many days, but do not know how, any help would be much oblidged. A cable company owns the roads marked with the dotted lines in ...
11
votes
3answers
240 views

How to compute $\int_0^\infty \frac{x^4}{(x^4+ x^2 +1)^3} dx =\frac{\pi}{48\sqrt{3}}$?

$$\int_0^\infty \frac{x^4}{(x^4+ x^2 +1)^3} dx =\frac{\pi}{48\sqrt{3}}$$ I have difficulty to evaluating above integrals. First I try the substitution $x^4 =t$ or $x^4 +x^2+1 =t$ but it makes ...
4
votes
3answers
109 views

Undetermined vs. Undefined [duplicate]

This often comes up in precalculus and calculus, that is sometimes an expression will be said to undefined while at other times undetermined. What is the fundamental difference between the two? For ...

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