User Phira - Mathematics Stack Exchange

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	12,169 reputation	bio	website		visits	member for	2 years, 1 month
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182

163

votes

23

answers

10

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Proofs that every mathematician should know?

soft-question big-list

mar 25 at 0:36 Glen O 3,177

39

131

votes

10

answers

29

kviews

Multiple-choice question about the probability of a random answer to itself being correct

homework probability

mar 25 at 20:45 Community♦ 1

82

131

votes

9

answers

8

kviews

What's an intuitive way to think about the determinant?

linear-algebra intuition determinant

may 13 at 7:14 MJD 21k

77

115

votes

28

answers

8

kviews

A challenge by R. P. Feynman: give counter-intuitive theorems that can be translated into everyday language

soft-question big-list examples-counterexamples

aug 6 at 1:40 John 1

30

70

votes

3

answers

3

kviews

What is the smallest number of $45^\circ-60^\circ-75^\circ$ triangles that a square can be divided into?

geometry puzzle recreational-mathematics open-problem tiling

mar 25 at 15:26 Ed Pegg 2,111

40

67

votes

5

answers

3

kviews

In (relatively) simple words: What is an inverse limit?

category-theory intuition universal-algebra

mar 29 at 8:55 Pieter Cuijpers 31

45

52

votes

21

answers

3

kviews

List of Interesting Math Blogs

soft-question big-list online-resources

apr 25 at 3:25 Bean 849

20

48

votes

2

answers

4

kviews

More than 99% of groups of order less than 2000 are of order 1024?

abstract-algebra combinatorics group-theory finite-groups p-groups

apr 15 at 20:46 Alexander Gruber♦ 15.2k

23

44

votes

3

answers

3

kviews

$\int_{-\infty}^{+\infty} e^{-x^2} dx$ with complex analysis

integral complex-analysis

jun 4 '11 at 12:45 night owl 975

17

40

votes

1

answer

1

kviews

What's the value of this Vieta-style product involving the golden ratio?

number-theory sequences-and-series

mar 28 '11 at 11:38 Community♦ 1

11

39

votes

4

answers

2

kviews

Double sum - Miklos Schweitzer 2010

sequences-and-series operator-theory divergent-series

jun 12 '11 at 2:49 Community♦ 1

7

36

votes

3

answers

2

kviews

$5^n+n$ is never prime?

number-theory prime-numbers

oct 4 '11 at 19:48 Charles 8,855

15

35

votes

5

answers

2

kviews

Find the average of $\sin^{100} (x)$ in 5 minutes?

approximation

oct 8 '11 at 14:53 Michael Hardy 48.2k

3

34

votes

2

answers

500

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Counting trails in a triangular grid

graph-theory combinatorics

may 7 '11 at 15:20 joriki 92.7k

6

34

votes

0

answers

669

views

How to think of the group ring as a Hopf algebra?

finite-groups representation-theory intuition hopf-algebras group-ring

may 1 at 10:08 Alexander Gruber♦ 15.2k

17

30

votes

2

answers

2

kviews

Intuitive reasoning behind $\pi$'s appearance in bouncing balls.

physics pi

may 8 '12 at 4:08 Michael Boratko 2,924

14

29

votes

4

answers

2

kviews

Finding the limit of $\frac {n}{\sqrt[n]{n!}}$

calculus homework

aug 4 at 15:17 Chris's wise sister 11.5k

13

29

votes

1

answer

1

kviews

$n!$ is never a perfect square if $n\geq2$. Is there a proof of this that doesn't use Chebyshev's theorem?

number-theory factorial alternative-proof

jan 31 '12 at 20:46 Srivatsan 15.6k

7

28

votes

3

answers

802

views

Why are there only a finite number of sporadic simple groups?

group-theory simple-groups

may 19 '11 at 8:51 ogerard 823

6

28

votes

6

answers

2

kviews

What is the larger of the two numbers?

algebra-precalculus inequality

jul 22 at 10:54 J. M. 38.9k

10

23

votes

3

answers

978

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Why is this series of square root of twos equal $\pi$?

sequences-and-series limit pi

dec 14 '11 at 16:54 J. M. 38.9k

8

22

votes

5

answers

884

views

Can every group be represented by a group of matrices?

group-theory representation-theory

nov 25 '11 at 11:23 user1729 3,354

5

21

votes

1

answer

575

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Purely combinatorial proof that$ (e^x)' = e^x$

combinatorics groupoids

apr 25 '12 at 22:56 t.b. 43.2k

8

21

votes

1

answer

445

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Rolling a Sphere on the Plane

geometry

apr 26 '11 at 4:57 joriki 92.7k

9

20

votes

3

answers

946

views

Set of continuity points of a real function

real-analysis general-topology measure-theory

nov 9 at 14:36 Elias 2,978

9

19

votes

2

answers

488

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Surprising but simple group theory result on conjugacy classes

homework group-theory representation-theory

may 12 '11 at 19:52 Nicky Hekster 2,677

6

17

votes

5

answers

2

kviews

Series converges implies $\lim{n a_n} = 0$

sequences-and-series

nov 23 '11 at 16:02 Pete L. Clark 44.6k

10

17

votes

1

answer

1

kviews

Proving that the sequence $F_{n}(x)=\sum\limits_{k=1}^{n} \frac{\sin{kx}}{k}$ is boundedly convergent on $\mathbb{R}$

real-analysis analysis sequences-and-series

dec 8 '10 at 6:54 Andrey Rekalo 3,554

9

16

votes

5

answers

2

kviews

How to prove that: $\tan(3\pi/11) + 4\sin(2\pi/11) = \sqrt{11}$

trigonometry

mar 22 '12 at 22:07 spanferkel 81

1

16

votes

4

answers

2

kviews

How can I prove that $\gcd(a,b)=1\implies \gcd(a^2,b^2)=1$ without using prime decomposition?

elementary-number-theory proof-strategy

sep 26 at 4:12 Community♦ 1

Phira

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