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Good Answer

Answer score of 25 or more. This badge can be awarded multiple times.

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Geometric intuition for the Stein factorization theorem?

Awarded Oct 23 at 20:52

Takumi Murayama

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How should I write proofs requiring complicated, yet routine, symbolic manipulation?

Awarded Oct 23 at 19:36

Yly

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Shortest path between two points on a surface

Awarded Oct 23 at 18:03

Plutoro

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Why is the statement "all vector space have a basis" equivalent to the axiom of choice?

Awarded Oct 23 at 14:08

Noah Schweber

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Solving $x^3-y^3=xy+61$ in integers

Awarded Oct 22 at 17:01

Christian Blatter

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Find all subgroups of $\mathbb{Z}\times\mathbb{Z}$.

Awarded Oct 22 at 8:45

Makoto Kato

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Infinite coproduct of affine schemes

Awarded Oct 22 at 5:15

Georges Elencwajg

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Proving the identity $\sum_{k=1}^n {k^3} = \big(\sum_{k=1}^n k\big)^2$ without induction

Awarded Oct 22 at 4:46

MafPrivate

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Planar geometry problems solved by thinking out of the plane

Awarded Oct 21 at 16:52

user8268

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

Awarded Oct 20 at 4:00

MintChocolate

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Is a submodule of a flat module flat?

Awarded Oct 19 at 22:05

Keenan Kidwell

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Best Fake Proofs? (A M.SE April Fools Day collection)

Awarded Oct 19 at 15:32

Yoni Rozenshein

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Intuition behind logarithm change of base

Awarded Oct 18 at 15:41

littleO

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When does the set enter set theory?

Awarded Oct 18 at 11:07

joseph.j.stern

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What is the difference between Lipschitz and general uniform continuity?

Awarded Oct 18 at 5:30

Severin Schraven

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Insightful proofs for Sherman-Morrison Formula and Matrix Determinant Lemma

Awarded Oct 16 at 4:06

Paul Hanson

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fundamental group of $GL^{+}_n(\mathbb{R})$

Awarded Oct 15 at 20:26

Qiaochu Yuan

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What's the rationale for requiring that a field be a *non-trivial* ring?

Awarded Oct 15 at 17:25

Andreas Blass

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Is there such a mathematical notion as 'antideterminant'?

Awarded Oct 15 at 15:23

Noah Schweber

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Is a function Lipschitz if and only if its derivative is bounded?

Awarded Oct 14 at 17:54

Three.OneFour

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order topology is Hausdorff

Awarded Oct 14 at 3:41

Brian M. Scott

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Five squares are next to each other. What is area of the shaded triangle?

Awarded Oct 12 at 11:34

fleablood

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Deriving the Surface Area of a Spherical Triangle

Awarded Oct 12 at 10:06

user8268

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With ZFC foundations, if all math objects are sets, where do these sets "live"?

Awarded Oct 11 at 11:40

Carl Mummert

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Correspondence theorem for rings.

Awarded Oct 10 at 12:05

Andrew Dudzik

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Geometric intuition for $\pi /4 = 1 - 1/3 + 1/5 - \cdots$?

Awarded Oct 10 at 10:26

leonbloy

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How to compute $\int_0^1\frac{\text{Li}_2(x^2)\arcsin^2(x)}{x}dx$ or $\sum_{n=1}^\infty\frac{4^nH_n}{n^4{2n\choose n}}$

Awarded Oct 10 at 6:25

Jorge Layja

quasi-compact and compact in algebraic geometry

Awarded Oct 9 at 8:18

Louis Deaett

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Existence of a local geodesic frame

Awarded Oct 8 at 17:42

user539719

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How can I prove formally that the projective plane is a Hausdorff space?

Awarded Oct 8 at 17:42

Makoto Kato

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Prove that $HK$ is a subgroup iff $HK=KH$.

Awarded Oct 8 at 5:42

Pedro♦

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

Awarded Oct 8 at 3:42

Ethan Bolker

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Show that $\int_{-\pi/2}^{\pi/2}\sin(\tan(\tan(x)))\tan(x)dx=\frac{\pi}{e^{(e^2-1)/(e^2+1)}}-\frac{\pi}{e}$

Awarded Oct 7 at 19:33

Sangchul Lee

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

Awarded Oct 7 at 11:56

Christophe Boilley

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

Awarded Oct 6 at 20:19

Linear Christmas

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The diameter of a compact set.

Awarded Oct 6 at 13:41

Norbert

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Computing $\int_{-\infty}^{\infty} \frac{\cos x}{x^{2} + a^{2}}dx$ using residue calculus

Awarded Oct 6 at 11:02

Mark Viola

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Why does $(A/I)\otimes_R (B/J)\cong(A\otimes_R B)/(I\otimes_R 1+1\otimes_R J)$?

Awarded Oct 5 at 13:02

Martin Brandenburg

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What's the easiest way to help a high schooler understand how to avoid the trap of extraneous and missing solutions?

Awarded Oct 5 at 10:15

jjagmath

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Understanding the assumptions in the Reverse Fatou's Lemma

Awarded Oct 4 at 23:06

anonymous

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Is it possible to construct a quasi-vectorial space without an identity element?

Awarded Oct 4 at 6:15

Arturo Magidin

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A complete subset of a metric space is closed?

Awarded Oct 3 at 4:42

shalin

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In what sense does a number "exist" if it is proven to be uncomputable?

Awarded Oct 2 at 17:46

Zhen Lin

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Set Theoretically, NOT CONCEPTUALLY, are Position Vectors the same as Points

Awarded Oct 1 at 16:52

Joe

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Do sum of natural numbers and sum of their squares represent uniquely the summands?

Awarded Sep 29 at 5:20

Oscar Lanzi

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Irreducible polynomial modulo every prime?

Awarded Sep 27 at 18:53

ShreevatsaR

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If a ring is Noetherian, then every subring is finitely generated?

Awarded Sep 27 at 9:22

Zev Chonoles

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Proof of the hockey stick/Zhu Shijie identity $\sum\limits_{t=0}^n \binom tk = \binom{n+1}{k+1}$

Awarded Sep 26 at 19:53

Hypergeometricx

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Why homology with coefficients?

Awarded Sep 26 at 15:07

Kevin Carlson

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Cyclic cyclotomic factor test e.g. split $14^7+14^2+1$ via $x^2\!+\!x\!+\!1\mid x^A\!+\! x^B\!+\! x^C\ \ {\rm if}\ \ \{A,B,C\}\equiv\{2,1,0\}\pmod{3}$

Awarded Sep 26 at 13:09

Bill Dubuque

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Proof of $\lim_{x\to a}f^{g}=e^{\lim_{x\to a}{(f-1)g}}$ when $\lim_{x\to a}f(x)=1$ and $\lim_{x\to a}g(x)=\infty$

Awarded Sep 26 at 6:02

zahbaz

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Show that $n$ lines separate the plane into $\frac{n^2+n+2}{2}$ regions

Awarded Sep 25 at 16:17

robjohn♦

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Calculate effective rank of matrix

Awarded Sep 24 at 22:31

Lionel Barnett

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Matrix exponential of a $3 \times 3$ skew-symmetric matrix without series expansion

Awarded Sep 24 at 14:25

JimmyK4542

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In a village, $90\%$ of people drink Tea, $80\%$ Coffee, $70\%$ Whiskey, $60\%$ Gin. Nobody drinks all four. What percentage of people drinks alcohol?

Awarded Sep 24 at 9:37

Key Flex

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Why are certain PDE called "elliptic", "hyperbolic", or "parabolic"?

Awarded Sep 24 at 4:23

CyclotomicField

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Calculating fundamental group of the Klein bottle

Awarded Sep 24 at 0:34

Jason DeVito - on hiatus

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Nice examples of groups which are not obviously groups

Awarded Sep 23 at 17:47

Tobias Kildetoft

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How can we prove $\pi =1+\frac{1}{2}+\frac{1}{3}+\frac{1}{4}-\frac{1}{5}+\frac{1}{6}+\frac{1}{7}+\cdots\,$?

Awarded Sep 23 at 17:17

Start wearing purple

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Automorphisms of the Petersen graph

Awarded Sep 22 at 3:41

Arturo Magidin

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