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Good Question

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Why is this allowed? ("Fourier's Trick"; finding the coefficients in a Fourier Series)

Awarded 17 hours ago

AmagicalFishy

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Examples for subspace of a normal space which is not normal

Awarded 2 days ago

Jesse P Francis

1,5674 gold badges28 silver badges75 bronze badges

How should a string be laid on a disk to minimize the expected shortest distance between a random point on the disk and the string?

Awarded Nov 18 at 17:03

Dan

40.3k5 gold badges83 silver badges246 bronze badges

Is an equivalence an adjunction?

Awarded Nov 17 at 9:21

sopot

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Is it possible to assign a value to the sum of primes?

Awarded Nov 15 at 19:12

Max Lonysa Muller

7,7782 gold badges39 silver badges80 bronze badges

What is the probability that $\sum_{k=1}^\infty\left(\prod_{i=1}^ku_i\right)>1$ where $u_i$ are random real numbers in $(0,1)$?

Awarded Nov 14 at 13:53

Dan

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If you create a power tower of all the digits in a number, calculate that out, and repeat this process, will you always reach a single digit number?

Awarded Nov 11 at 20:46

Nico Zaczkowski

1,4692 silver badges13 bronze badges

Is $\mathbb Z _p^*=\{ 1, 2, 3, ... , p-1 \}$ a cyclic group?

Awarded Nov 8 at 18:49

HK Lee

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Professor insists $-0$ does not exist, am I crazy?

Awarded Nov 7 at 1:10

Obo the Hobo

3751 silver badge5 bronze badges

The categories Set and Ens

Awarded Nov 6 at 23:06

Zhen Lin

98.6k15 gold badges207 silver badges362 bronze badges

What is the smallest polyomino that can't surround a $1\times 1$ hole?

Awarded Nov 6 at 12:21

RavenclawPrefect

19.1k3 gold badges42 silver badges112 bronze badges

Why do elementary row operations preserve linear dependence between matrix columns?

Awarded Nov 4 at 9:18

Matthew Hampsey

7152 gold badges7 silver badges18 bronze badges

Fundamental group is abelian iff the fundamental group isomorphisms (a-hat) coincide

Awarded Nov 3 at 14:36

thobanster

1,0712 gold badges11 silver badges16 bronze badges

Combinatorial proof of $\sum\limits_{k=0}^n {n \choose k}3^k=4^n$

Awarded Nov 1 at 20:48

MichaelS

8832 gold badges9 silver badges18 bronze badges

Why doesn't a simple mean give the position of a centroid in a polygon?

Awarded Oct 30 at 22:49

Lazer

1,6254 gold badges18 silver badges19 bronze badges

How a principal bundle and the associated vector bundle determine each other

Awarded Oct 29 at 18:06

GFR

5,64123 silver badges38 bronze badges

Do moments define distributions?

Awarded Oct 29 at 2:48

Ant

21.6k6 gold badges52 silver badges104 bronze badges

Maximizing $\int_0^1 f(x) \, {\rm d} x$ given $\int_0^1 x f(x) \, {\rm d} x = 0$

Awarded Oct 28 at 23:34

Amogh Gajera

4591 silver badge7 bronze badges

What are some modern books on Markov Chains with plenty of good exercises?

Awarded Oct 28 at 3:27

Landon Carter

13.5k4 gold badges38 silver badges93 bronze badges

Evaluate $\int_{0}^{\pi/4}x\ln^{2}(\sin(x))dx$

Awarded Oct 26 at 12:55

Cody

14.5k40 silver badges104 bronze badges

What's an example of a theory that's consistent yet has no model?

Awarded Oct 25 at 7:36

user114806

5794 silver badges9 bronze badges

I think I don't truly understand Cauchy's Integral theorem

Awarded Oct 24 at 20:18

SunnyMath

3593 silver badges5 bronze badges

What is the codimension of matrices of rank $r$ as a manifold?

Awarded Oct 24 at 1:00

Geovanna Anthony

6896 silver badges12 bronze badges

Real-valued 2D Fourier series?

Awarded Oct 22 at 18:34

Benno

1,7161 gold badge16 silver badges22 bronze badges

Factorize the polynomial $x^3+y^3+z^3-3xyz$

Awarded Oct 22 at 15:12

AaronS

1,2982 gold badges13 silver badges30 bronze badges

Simple proof of Cauchy's theorem in Group theory

Awarded Oct 22 at 12:08

adone

3591 gold badge3 silver badges3 bronze badges

Given the graph $y=x^4$, can we construct the $y$-axis using only a straightedge and a compass?

Awarded Oct 21 at 19:51

praton

9333 silver badges13 bronze badges

Planar geometry problems solved by thinking out of the plane

Awarded Oct 21 at 15:01

Dan

40.3k5 gold badges83 silver badges246 bronze badges

How much do you eat from the cake with the best frosting?

Awarded Oct 20 at 20:41

fox

5419 silver badges22 bronze badges

Minimum operations to find tangent to circle

Awarded Oct 20 at 9:01

Gillespie

3651 gold badge3 silver badges6 bronze badges

What even *are* elliptic functions?

Awarded Oct 17 at 8:23

clathratus

18.3k4 gold badges33 silver badges92 bronze badges

What planar convex shape maximizes the probability that a random circle contains the centre? (Surprisingly, it's not a disk.)

Awarded Oct 16 at 15:10

Dan

40.3k5 gold badges83 silver badges246 bronze badges

Monster integral without complex argument $\arcsin$: $\int^1_0 \frac{\arccos(x)}{x}f(x^2) dx =\frac{\pi^4}{512}$

Awarded Oct 16 at 3:05

epsilon

3,1561 gold badge5 silver badges42 bronze badges

In written mathematics, is $f(x)$a function or a number?

Awarded Oct 13 at 4:09

janmr

3533 silver badges11 bronze badges

How to see the real projective plane is a Möbius band glued to a disk?

Awarded Oct 12 at 14:26

Joseph O'Rourke

31.2k4 gold badges85 silver badges173 bronze badges

Trigonometic Substitution VS Hyperbolic substitution

Awarded Oct 10 at 18:52

krismath

4051 gold badge6 silver badges10 bronze badges

Cartesian product of compact sets is compact

Awarded Oct 10 at 3:27

user108701

3531 gold badge4 silver badges12 bronze badges

The most generic radicals-solvable quintic

Awarded Oct 8 at 17:27

Alma Do

7474 silver badges12 bronze badges

Open subgroups of a topological group are closed

Awarded Oct 8 at 13:33

Myshkin

37.1k28 gold badges173 silver badges351 bronze badges

Imaginary part of $\int_{0}^{\pi/2} \frac{x^2}{x^2+\log ^2(-2\cos x)} \:\mathrm{d}x$ and $\int_{0}^{\pi/2} \frac{\log \cos x}{x^2}\:\mathrm{d}x$

Awarded Oct 8 at 9:42

Olivier Oloa

123k19 gold badges208 silver badges329 bronze badges

Is every factorial divisible by its sum of digits?

Awarded Oct 8 at 8:47

R B

2,4761 gold badge25 silver badges40 bronze badges

Why do we consider there to be gaps between rational numbers, and not between real numbers?

Awarded Oct 8 at 2:25

some kid trying her best

1,1854 silver badges11 bronze badges

How do French mathematicians write ordered pairs, since they already use the comma as a decimal separator?

Awarded Oct 7 at 18:15

Pineapple Fish

2,6151 gold badge16 silver badges33 bronze badges

Generalization of "easy" 1-D proof of Brouwer fixed point theorem

Awarded Oct 7 at 17:03

Lopsy

4,65024 silver badges28 bronze badges

How to understand/remember Hölder's inequality

Awarded Oct 3 at 20:38

John

13.8k2 gold badges37 silver badges64 bronze badges

What is the probability that a plane through three random points on the surface of the Earth intersects the Moon?

Awarded Oct 3 at 10:47

Dan

40.3k5 gold badges83 silver badges246 bronze badges

Prove that the Lie derivative of a vector field equals the Lie bracket: $\frac{d}{dt} ((\phi_{-t})_* Y)|_{t=0} = [X,Y]$

Awarded Oct 1 at 22:32

user15464

12.2k4 gold badges56 silver badges108 bronze badges

What is the name of the vertical bar in $(x^2+1)\vert_{x = 4}$ or $\left.\left(\frac{x^3}{3}+x+c\right) \right\vert_0^4$?

Awarded Oct 1 at 9:12

OghmaOsiris

1,0493 gold badges12 silver badges22 bronze badges

Can this be done without a calculator? Show that $\int_0^1(1-x^2)(1-x^4)(1-x^6)\dots dx<\frac{1}{\sqrt3}$

Awarded Sep 28 at 16:20

Dan

40.3k5 gold badges83 silver badges246 bronze badges

Intuitive explanation of Duhamel's principle

Awarded Sep 25 at 19:01

JLA

7,0022 gold badges29 silver badges43 bronze badges

Understanding the proof of $l_2$ being complete.

Awarded Sep 25 at 5:49

titusAdam

2,9872 gold badges18 silver badges48 bronze badges

Prove the inequality $\frac{b+c}{a(y+z)}+\frac{c+a}{b(z+x)}+\frac{a+b}{c(x+y)}\geq \frac{3(a+b+c)}{ax+by+cz}$

Awarded Sep 24 at 6:48

Mathis

9577 silver badges17 bronze badges

Proving that every isometry of $\mathbb{R}^n$ is of the form of a composition of at most $n+1$ reflections

Awarded Sep 22 at 13:24

Belgi

23.7k18 gold badges101 silver badges169 bronze badges

Perfect Map $p:\ X\to Y$, $Y$ compact implies $X$ compact

Awarded Sep 21 at 5:07

KarlG

6411 gold badge6 silver badges14 bronze badges

Non-trivial zero(s) of Akiyama-Tanigawa triangle

Awarded Sep 20 at 0:09

Integrand

7,71416 gold badges50 silver badges78 bronze badges

Is the Collatz conjecture in $\Sigma_1 / \Pi_1$?

Awarded Sep 18 at 22:35

Steven Stadnicki

53.4k9 gold badges91 silver badges156 bronze badges

What would a base $\pi$ number system look like?

Awarded Sep 17 at 20:05

Luke Machowski

4271 gold badge5 silver badges8 bronze badges

Dirac delta in polar coordinates

Awarded Sep 14 at 14:56

JFNJr

1,1052 gold badges11 silver badges24 bronze badges

Mickey Mouse Polygon - Regular Polygons forming Mysterious Angle

Awarded Sep 14 at 14:09

Chris So

6812 silver badges9 bronze badges

The law of the unconscious statistician

Awarded Sep 13 at 13:11

Jori

1,8381 gold badge17 silver badges33 bronze badges

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