User Joe - Mathematics Stack Exchange

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	761 reputation	bio	website		visits	member for	7 months
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5

votes

2

answers

82

views

Why do people use “K” to represent a complete graph?

graph-theory notation

35m ago Zev Chonoles 54k

1

vote

2

answers

282

views

What's the relationship between interior/exterior/boundary point and limit point?

real-analysis

jan 10 at 8:47 Stefan Hansen 8,563

1

vote

3

answers

135

views

Real Analysis: Is $\emptyset$ a open set in $X$?

real-analysis

jan 10 at 3:57 Community♦ 1

5

votes

2

answers

136

views

What is the difference between open ball and neighborhood in real analysis?

real-analysis

jan 9 at 16:47 Ilya 14.2k

3

7

votes

1

answer

199

views

How to geometrically interpret $\sum^{p}_{1}\lambda_{i}(A)=\operatorname{tr}(A)$?

linear-algebra

dec 23 at 22:49 Amzoti 14.1k

5

9

votes

1

answer

508

views

How to understand spectral decomposition geometrically

linear-algebra geometry matrices spectral-theory

dec 4 at 14:03 Javier Álvarez 4,794

2

votes

3

answers

285

views

Soft question: Why freshmen feel linear algebra is abstract?

linear-algebra soft-question

nov 25 at 10:22 Joe 761

0

votes

2

answers

77

views

Calculating variance, how to determine when to use 1/n or 1/(n-1)?

statistics

nov 26 at 3:25 Michael Hardy 48.2k

6

13

votes

3

answers

880

views

How to intuitively understand eigenvalue and eigenvector?

linear-algebra statistics

nov 24 at 9:01 Joe 761

2

votes

1

answer

152

views

What's the relationship between Cauchy-Schwarz Inequality and Extended Cauchy-Schwarz Inequality?

linear-algebra

nov 17 at 15:09 Berci 20.7k

6

votes

4

answers

265

views

What is degree of freedom in statistics?

statistics

nov 15 at 12:06 Gottfried Helms 7,217

2

5

votes

2

answers

97

views

Why $\sigma_{\bar{x}}=\frac{\sigma}{\sqrt{n}}$

statistics

nov 14 at 11:03 Ivan Lerner 491

2

votes

1

answer

102

views

How to prove in a graph $G$, its incidence matrix $A$ is totally unimodular if and only if $G$ is a bipartite graph?

reference-request graph-theory

nov 16 at 21:38 TMM 7,156

1

vote

1

answer

93

views

Let $\cos (bx)-\sin ^2(x)-1=0$ has no zero point except 0. What's the value of b?

trigonometry complex-numbers

nov 5 at 14:56 Adi Dani 5,977

-1

votes

2

answers

185

views

How many complex numbers satisfy $z\bar{z}=1$?

complex-numbers

nov 5 at 14:38 Peter Tamaroff 25.9k

0

votes

1

answer

143

views

Let $x,y,z$ be independent uniform distribution on $(0,\pi)$. What's the probability that $z\leq \cos^2(x)\sin^2(y)$?

probability

nov 5 at 14:10 anonymous 649

0

votes

2

answers

51

views

Let $\frac{dy}{dx}-\frac{y}{x}=xe^{-x}$. Find $\lim_{x \to \infty}\frac{y}{x}$

calculus

nov 5 at 12:43 Harald Hanche-Olsen 10.5k

0

votes

1

answer

78

views

Find the arc length of $\frac{dy}{dx}=\sqrt{(1-x)^2+1}$

calculus

nov 5 at 12:46 Babak S. 27.9k

0

votes

1

answer

73

views

Let $y+xy'=x$, $y(0)=-1$. Find $\lim_{x \to \infty}y(x)$

calculus

nov 3 at 16:11 amWhy 55k

1

vote

2

answers

150

views

What is the largest order of element in an abelian group of order $5!$?

abstract-algebra group-theory abelian-groups

nov 3 at 17:03 Alexander Gruber♦ 15.2k

0

votes

2

answers

190

views

How many solutions does $\cos(97x)=x$ have?

trigonometry functions

nov 3 at 16:50 Jean-Sébastien 2,257

2

votes

2

answers

108

views

Let $f'(0)=f''(0)=1$, $f^{(12)}(x)$ is differentiable and $g=f(x^{10})$ What's the value of $g^{(11)}(0)$?

calculus

nov 9 at 10:47 P.. 8,905

4

votes

3

answers

212

views

Can $11^{13}-1$ be divided exactly by 6?

number-theory

nov 2 at 18:43 Haskell Curry 11.1k

1

vote

4

answers

275

views

Which letter is not homeomorphic to the letter $C$?

general-topology algebraic-topology

nov 1 at 16:40 Matt N. 15.3k

1

vote

2

answers

85

views

How to quickly judge a function is injection?

calculus real-analysis

oct 30 at 17:25 Brian M. Scott 155k

1

2

votes

2

answers

48

views

Maps $g$ maps $\left\{1,2,3,4,5\right\}$ onto $\left\{11,12,13,14\right\}$ and $g(1)\neq g(2)$. How many g are there.

combinatorics

oct 29 at 16:26 Max Morin 751

1

vote

1

answer

36

views

What's the distribution of a row in a normal distributed data?

homework statistics

oct 29 at 12:17 Simon Hayward 572

0

votes

2

answers

89

views

How many components of complement of a compact and connected set in $\mathbb{R^2}$has?

general-topology

oct 29 at 3:54 Brian M. Scott 155k

0

votes

2

answers

122

views

$f$ is a continuous function $\mathbb{X}\to\mathbb{X}$, does $f$ necessarily has fixed point?

general-topology

oct 29 at 19:49 Joe 761

0

votes

1

answer

56

views

Find $\int_{C}\frac{e^{\pi z}}{\frac{(z-4i)^2}{z-i}}dz$

calculus complex-numbers

oct 29 at 15:05 Simon Hayward 572

Joe

56 Questions