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Nice Answer

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Does "the preimage of a closed interval is a finite union of closed intervals" imply $f:\mathbb{R}\to\mathbb{R}$ is continuous?

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Dermot Craddock

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How do I prove that $\det A= \det A^T$?

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Daan Michiels

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Prove regular language closed under min and max

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Brian M. Scott

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Is this a known theorem?

Awarded 17 hours ago

Edward Porcella

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Is $\varphi = \frac{3\cdot 7\cdot 11\cdot\dots\cdot 599}{5\cdot 9\cdot 13\cdot\dots\cdot 601}$ greater than, less than, or equal to $\frac{1}{13}$?

Awarded 17 hours ago

2'5 9'2

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Connected components of a scheme are irreducible

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Rankeya

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Evaluate $\int_0^{\frac\pi2}\frac{\mathrm dx}{a\sin ^2x+b\cos ^2x}$ without using its antiderivative

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Travis Willse

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One question to know if the number is 1, 2 or 3

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chubakueno

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Prove $\int_0^af(x)\mathrm dx\ge a\int_0^1f(x)\mathrm dx$ for decreasing function

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Martin R

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How to set the limits of a definite integral by substitution?

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CP of Physics

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A subset of a rectangle that 'blocks' every curve that goes from right to left must connect upper and lower sides

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Dennis

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"Moral" difference between Poincare and Sobolev inequalities

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Gio67

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Does this characterize the product topology?

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Joshua Tilley

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Is there any way to represent an imaginary number?

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André Nicolas

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Sufficient / necessary conditions for $g \circ f$ being injective, surjective or bijective

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Mikasa

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Inductive proof that ${2n\choose n}=\sum{n\choose i}^2.$

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Ishan Banerjee

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What is $\lim_n \sqrt[n]{1+\cos(n)}$?

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Dermot Craddock

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Can you prove equality of two expressions by setting them equal in an equation?

Awarded Nov 27 at 23:45

Pedro

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What comes after diagram chasing?

Awarded Nov 27 at 20:12

Brian Fitzpatrick

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Analytic Applications of Stone-Čech compactification

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Qiaochu Yuan

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$xy-zw$ is an irrreducible element in $\mathbb C[x,y,z,w]$

Awarded Nov 27 at 14:57

Marc van Leeuwen

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How far can an infinite number of unit length planks bridge a right-angled gap?

Awarded Nov 27 at 5:25

AccidentalTaylorExpansion

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How far can an infinite number of unit length planks bridge a right-angled gap?

Awarded Nov 26 at 21:18

mathperson314

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Definition of homogeneous ideal

Awarded Nov 26 at 17:53

Andrew Dudzik

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Good book for mathematical modeling

Awarded Nov 26 at 17:23

etothepitimesi

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Simplicity of $A_n$

Awarded Nov 26 at 14:12

p Groups

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Why is the trace of a matrix important?

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KBS

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Can an element in a ring with unity be both a unit and zero-divisor?

Awarded Nov 26 at 11:08

Asinomás

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In Godel's first incompleteness theorem, what is the appropriate notion of interpretation function?

Awarded Nov 26 at 4:22

user21820

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Show that $\int_0^{\infty}\frac{\operatorname{Li}_s(-x)}{x^{\alpha+1}}\mathrm dx=-\frac1{\alpha^s}\frac{\pi}{\sin(\pi \alpha)}$

Awarded Nov 26 at 1:23

pisco

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An open subset of a manifold is a manifold

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Rasmus

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Are $C^\infty$ exotic spheres $C^k$ exotic?

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anomaly

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Can there be a continuous function with infinite derivative everywhere?

Awarded Nov 25 at 13:30

D.R.

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Can there be a continuous function with infinite derivative everywhere?

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Martin R

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How to calculate $\arctan(\sqrt3-2)$ to be $-15°$ by hand?

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Empy2

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Funny identities

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ZHN

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Solving for $x$ when $x$ is the denominator

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Austin Mohr

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What makes higher/second-order logic incompatible with completeness theorem?

Awarded Nov 24 at 18:07

André Nicolas

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Existence of k-regular graph

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Yuval Filmus

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Condition number for polynomial interpolation matrix

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user1551

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Can $1, \sqrt{26},5$ construct a right angle triangle?

Awarded Nov 24 at 0:25

Anne Bauval

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Solve recurrence for strings that do not contain the substring 101

Awarded Nov 23 at 16:48

Markus Scheuer

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Why Is the Dual Basis Mathematically Unavoidable?

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Andreas Blass

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How "big" can the center of a finite perfect group be?

Awarded Nov 23 at 13:55

mesel

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How "big" can the center of a finite perfect group be?

Awarded Nov 23 at 13:55

Derek Holt

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Are one-point sets always compact in any topological spaces?

Awarded Nov 23 at 12:36

Andres Mejia

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Find the number of subsets $A$ of $S= \{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 \}$ such that: $x\in A\wedge 2x\in S\implies 2x \in A$

Awarded Nov 23 at 12:36

Ross Millikan

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Evaluate: $4^9-\binom{8}{1}4^8+\binom{7}{2}4^7-\binom{6}{3}4^6+\binom{5}{4}4^5$

Awarded Nov 23 at 0:02

匚ㄖㄥᗪ乇ᗪ

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Trouble understanding proof to $\vdash ((\neg(\phi\rightarrow \psi))\rightarrow\phi)$?

Awarded Nov 22 at 18:30

Taroccoesbrocco

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Are these two definitions of base for a topology equivalent?

Awarded Nov 22 at 14:52

Lee Mosher

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What is the correct definition of a limit point in real analysis?

Awarded Nov 22 at 12:41

Matthew Leingang

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Let $G$ be a group of order $56$. Then which of the following are true

Awarded Nov 22 at 12:08

Alexander Gruber♦

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What are the subobjects of a manifold?

Awarded Nov 22 at 10:22

Makoto Kato

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Intuitive explanation of why the modified Gram-Schmidt is more stable than the classical one?

Awarded Nov 22 at 6:33

rpm2718

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show that $\int_{0}^{\infty} \frac {\sin^3(x)}{x^3}dx=\frac{3\pi}{8}$

Awarded Nov 22 at 2:50

Ivo Terek

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Show $\sum_{n=0}^\infty\frac{1}{a^2+n^2}=\frac{1+a\pi\coth a\pi}{2a^2}$

Awarded Nov 22 at 2:50

Jack D'Aurizio

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Is the transfer principle useless?

Awarded Nov 21 at 23:05

Henry

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Is this formula for cosine correct? (And is it significant)

Awarded Nov 21 at 22:51

Claude Leibovici

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Closed form for $f(x)=\ _3F_2\left(\tfrac12,\tfrac12,\tfrac12;\tfrac32,\tfrac32;x\right)$

Awarded Nov 21 at 21:04

ComplexYetTrivial

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Are ceiling and floor elementary functions?

Awarded Nov 21 at 18:49

Jair Taylor

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