User crf - Mathematics Stack Exchange

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5

17

votes

8

answers

656

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What is it about modern set theory that prevents us from defining the set of all sets which are not members of themselves?

set-theory

aug 17 at 20:48 Hurkyl 21.6k

1

10

votes

9

answers

272

views

Why is it legit to evaluate $\lim_{x\rightarrow 1} \frac{(x-1)(x+1)}{x-1}$ by cancelling common factors?

limit

feb 6 at 22:51 MiauPiau 6

1

6

votes

3

answers

193

views

Help understanding $e^{it}=\cos t+i\sin t$ by way of matrices and vector fields

sep 5 at 7:04 crf 1,116

2

5

votes

3

answers

158

views

Is a broken clock right twice a day?

periodic-functions

mar 31 at 8:21 Christian Blatter 32.7k

4

5

votes

2

answers

130

views

When does the next bus come?

probability queueing-theory

mar 28 at 5:01 Joe Turner 353

1

5

votes

2

answers

120

views

Calculate $\left\Vert \begin{bmatrix}1 & 2\\ 2 & 4 \end{bmatrix} \right\Vert$

linear-algebra matrices norm

jan 8 at 7:19 user17762 76.9k

5

votes

2

answers

101

views

Why does it always take n numbers to characterize a point in n-dimensional space (or does it)?

coordinate-systems polar-coordinates

jun 8 '12 at 20:12 Qiaochu Yuan 118k

4

votes

0

answers

48

views

Prove a function has $k$ continuous derivatives from its Fourier series

homework fourier-series

mar 27 at 4:59 crf 1,116

1

4

votes

4

answers

501

views

Let X and Y be random variables with joint pdf $f(x,y)=x+y$ for $0<x<1$ and $0<y<1$. Are X and Y independent? My heart says yes but my math says no.

homework probability

aug 12 at 3:38 Ikuyasu 12

2

3

votes

3

answers

184

views

Is there a quicker, nicer way to show that the union of compact sets is not necessarily compact?

homework real-analysis general-topology

mar 1 at 15:50 TonyK 11.9k

1

3

votes

1

answer

106

views

Show that the Riemann-Stieltjes integral exists

homework real-analysis integral

jan 16 at 8:44 lyj 1,416

3

votes

1

answer

88

views

Why does maximum likelihood estimation work the way that it does?

probability statistics

dec 24 at 3:24 Bryce 291

3

votes

1

answer

46

views

An example of a series in which using $\limsup$ rather than $\lim$ in performing the root test or the ratio test would make a difference?

real-analysis sequences-and-series convergence

nov 4 at 5:04 André Nicolas 162k

3

votes

2

answers

192

views

Interesting or non-obvious finite subsets of the natural numbers

elementary-number-theory soft-question natural-numbers

sep 12 at 10:56 Sean Eberhard 2,708

3

votes

1

answer

86

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Show that if X is a discrete random variable such that for nonnegative integers m,n, $P(X>m+n|X>m)=P(X>n)$, then X is geometric

homework probability probability-distributions

jul 31 at 15:12 Sasha 41.4k

3

votes

1

answer

393

views

Two related questions about flipping a coin an infinite number of times

probability-theory

apr 16 '12 at 2:28 Jim Belk 13.7k

3

votes

2

answers

94

views

Probability that judges are right about their verdict

homework probability

apr 15 '12 at 19:17 André Nicolas 162k

3

votes

2

answers

55

views

A question about subspaces

homework linear-algebra vector-spaces

nov 1 '11 at 8:02 Ashok 745

2

votes

1

answer

49

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Is there a nice way to interpret this matrix equation that comes up in the context of least squares

linear-algebra interpolation

may 17 at 7:14 Landscape 7,810

2

votes

2

answers

42

views

Why do we need $A$ to have linearly independent columns in order for $P_A=A(A^TA)^{-1}A^T$ to hold?

linear-algebra

apr 16 at 6:58 srijan 3,765

1

2

votes

2

answers

48

views

Prove that if $\sum c_n e^{inx}$ converges in $L^2$ to $f$ then $c_n$ are the Fourier coefficients.

homework real-analysis fourier-series

apr 5 at 18:05 Ju'x 2,944

2

votes

3

answers

60

views

Why is MATLAB giving me these weird eigenvectors?

homework linear-algebra matlab eigenvectors

apr 3 at 4:12 Bitwise 356

2

votes

0

answers

62

views

Property of an algebra of continuous functions on a compact set which separates points

homework real-analysis functional-analysis

mar 13 at 5:33 crf 1,116

1

2

votes

1

answer

38

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Prove $I:C([0,1])\rightarrow C([0,1])$ defined by $I(f)(x)=\int_0^x f(t)dt$ is uniformly continuous

homework real-analysis continuity

mar 1 at 4:11 julien 23.2k

2

votes

1

answer

57

views

What is meant by the word ‘control’ in the context of analysis?

real-analysis terminology

feb 7 at 18:22 Haskell Curry 11.1k

2

votes

1

answer

236

views

Prove that if $f$ is Riemann-Integrable on $ [0,1]$ then $\lim_{c\rightarrow 0} \int_c^1 f(x)dx$ exists and is equal to $\int_0^1 f(x)dx$

homework real-analysis integral limit improper-integrals

jan 28 at 9:58 Thomas 1,223

2

votes

1

answer

171

views

Proving Hölder's Inequality

homework real-analysis integral inequality

jan 25 at 7:05 Paul 8,672

2

votes

2

answers

560

views

Prove that $f(x)=x$ is Riemann-integrable on $[0,1]$ with $\int_0^1xdx=\frac{1}{2}$

homework real-analysis integration

jan 11 at 7:24 proximal 2,229

2

votes

2

answers

203

views

Baby Rudin problem 3.22: prove Baire's theorem. Am I going in a reasonable direction?

homework real-analysis general-topology baire-category

dec 25 at 22:04 BenjaLim 16.9k

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2

votes

2

answers

55

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Given the first $n$ terms of a sequence, can we find a function which would generate any infinite sequence we like that has the same first $n$ terms?

sequences-and-series

dec 5 at 8:55 Gunnar Magnusson 1,556

crf

59 Questions