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General Q&A about all branches of theoretical and applied mathematics, including closely-adjacent sciences where the central question is about the math.

377 posts RSS
Activity Age Score Random
Filters (None)
71%
+3 −0
Do linear and group invariant functions allowed to go inside(?) integral operators?

1 answer  ·  posted 2y ago by sepiabrown‭  ·  last activity 2y ago by r~~‭

integration geometric-deep-learning invariant-function
14%
+0 −10
How can 3/1 ≡ 1/(1/3), when left side features merely integers, but right side features a repetend?

2 answers  ·  posted 2y ago by Chgg Clou‭  ·  last activity 2y ago by Snoopy‭

arithmetical-hierarchy
80%
+6 −0
Does there exist a non-zero game such that the sum of three or more copies of it is zero?

0 answers  ·  posted 2y ago by celtschk‭

combinatorial-game-theory
77%
+5 −0
Why can't we conclude the extrema property of a function from its quadratic approximation when the discriminant is zero?

1 answer  ·  posted 2y ago by Snoopy‭  ·  last activity 2y ago by Snoopy‭

multivariable-calculus derivatives
71%
+3 −0
How to calculate remaining volume of a wire spool

2 answers  ·  posted 2y ago by re89j‭  ·  last activity 2y ago by Olin Lathrop‭

geometry volume
37%
+1 −3
What's wrong with evaluating $n(n-1) \dots (n-[k-3])(n-[k-2])\color{red}{(n-[k-1])}$ at $k = 1$?

1 answer  ·  posted 4y ago by DNB‭  ·  edited 2y ago by Peter Taylor‭

notation
75%
+4 −0
Product of empty set of elements vs. product over empty indexing set — is there any difference?

1 answer  ·  posted 4y ago by The Amplitwist‭  ·  edited 2y ago by Peter Taylor‭

product definition notation algebra
71%
+3 −0
Finding distance to parabola's focus, given some points

1 answer  ·  posted 3y ago by msh210‭  ·  edited 2y ago by Peter Taylor‭

geometry conics
71%
+3 −0
Show that $\forall n \in \mathbb{Z}^{+}$, $25^n \equiv 25 \bmod{100}$.

2 answers  ·  posted 2y ago by Carefree Explorer‭  ·  edited 2y ago by Peter Taylor‭

number-theory recreational-mathematics modular-arithmetic
75%
+4 −0
Proving that $p\mid (p+1776)$ if $p$ is a prime and $p(p+1776)$ is a perfect square

2 answers  ·  posted 2y ago by Snoopy‭  ·  last activity 2y ago by Snoopy‭

number-theory algebra
71%
+3 −0
organizing a library

1 answer  ·  posted 2y ago by msh210‭  ·  last activity 2y ago by celtschk‭

combinatorics recreational-mathematics
75%
+4 −0
If $\mathbf{R}$ is thought of as a vector space over $\mathbf{Q}$, what is its dimension?

1 answer  ·  posted 2y ago by Snoopy‭  ·  last activity 2y ago by r~~‭

linear-algebra vector-space
33%
+0 −2
Inhomogenous differential equations in sciences

0 answers  ·  posted 2y ago by MissMulan‭  ·  edited 2y ago by MissMulan‭

calculus equation differential applied-mathematics
71%
+3 −0
Prove $e^x \ge x+1 \\\; \forall x \in \mathbb{R}$ using induction

1 answer  ·  posted 3y ago by Carefree Explorer‭  ·  edited 3y ago by Derek Elkins‭

limits induction inequality solution-verification
50%
+0 −0
Is there a way to encode a unique arrangement of vertices of a graph with a unique short word?

2 answers  ·  posted 3y ago by Carefree Explorer‭  ·  last activity 3y ago by celtschk‭

graph-theory
71%
+3 −0
Show that $f(x) = \arctan\left(\frac{x}{x+1}\right) + \arctan\left(\frac{x+1}{x}\right) = \frac{\pi}{2}$

2 answers  ·  posted 3y ago by Carefree Explorer‭  ·  last activity 3y ago by Derek Elkins‭

limits trigonometry
60%
+1 −0
What's the common ratio for this geometric sequence?

1 answer  ·  posted 3y ago by General Sebast1an‭  ·  last activity 3y ago by tommi‭

geometric-sequence sequence
71%
+3 −0
The gcd of powers in a gcd domain

0 answers  ·  posted 3y ago by Snoopy‭  ·  edited 3y ago by Snoopy‭

abstract-algebra
50%
+3 −3
Isn't "any, some, or all" redundant? Why not write just "any"?

1 answer  ·  posted 3y ago by Chgg Clou‭  ·  last activity 3y ago by Tim Pederick‭

terminology
50%
+0 −0
What are the 2 arithmetic means of $x + y$ and $4x - 2y$?

2 answers  ·  posted 3y ago by General Sebast1an‭  ·  last activity 3y ago by General Sebast1an‭

arithmetic sequence mean
71%
+3 −0
Notation for nested exponents

1 answer  ·  posted 3y ago by JRN‭  ·  last activity 3y ago by leovt‭

notation exponents
70%
+5 −1
equilateral triangle inscribed in an ellipse

2 answers  ·  posted 3y ago by msh210‭  ·  last activity 3y ago by Anonymous‭

conics triangle
71%
+3 −0
Do the Faber partition polynomials have integer coefficients?

1 answer  ·  posted 3y ago by Peter Taylor‭  ·  last activity 3y ago by Peter Taylor‭

combinatorics generating-functions polynomials
30%
+1 −5
In "if and only if" proofs, why's 1 direction easier to prove than the other?

2 answers  ·  posted 4y ago by Chgg Clou‭  ·  last activity 3y ago by Prime Mover‭

logic
75%
+4 −0
Optimising a 3 value problem (well 2 really)

1 answer  ·  posted 3y ago by KalleMP‭  ·  last activity 3y ago by Peter Taylor‭

analysis formula algorithm
86%
+11 −0
Complex numbers in 2D, quaternions in 4D, why nothing in 3D?

2 answers  ·  posted 3y ago by Fred Wamsley‭  ·  last activity 3y ago by Derek Elkins‭

quaternions
60%
+1 −0
How $ijk=\sqrt{1}$?

2 answers  ·  posted 3y ago by deleted user  ·  last activity 3y ago by Tim Pederick‭

quaternions
80%
+6 −0
$g(x)\xrightarrow{x\to\infty}\infty$ Implies $g'(x)\leq g^{1+\varepsilon}(x)$

3 answers  ·  posted 3y ago by Udi Fogiel‭  ·  last activity 3y ago by Peter Taylor‭

calculus
60%
+1 −0
Are vectrices useful for calculations as opposed to formalism?

1 answer  ·  posted 3y ago by Fred Wamsley‭  ·  last activity 3y ago by Derek Elkins‭

Vectrix Numerical
33%
+0 −2
How to intuit p = Calvin's probability of winning each game independently = $1/2 \implies$ P(Calvin wins the match) = 1/2?

1 answer  ·  posted 3y ago by DNB‭  ·  last activity 3y ago by viäränlaenen‭

probability
71%
+3 −0
Matrices with rotational symmetry

1 answer  ·  posted 3y ago by Peter Taylor‭  ·  last activity 3y ago by Peter Taylor‭

linear-algebra matrices
50%
+0 −0
Why does the Dottie number $=\sqrt{1-\left(2\text I^{-1}_\frac12\left(\frac12,\frac32\right)-1\right)^2}$?

0 answers  ·  posted 3y ago by Tyma Gaidash‭  ·  edited 3y ago by Tyma Gaidash‭

probability equation median inverse
50%
+0 −0
A discrete-time queue Markov Chain problem

0 answers  ·  posted 3y ago by Joe‭

Markov-chains
50%
+0 −0
How can I justify whether I'm able to apply the Gaussian elimination method to this system?

1 answer  ·  posted 3y ago by dumplings‭  ·  edited 3y ago by Peter Taylor‭

equation system gaussian
50%
+0 −0
Sample skewness consistency [closed]

0 answers  ·  posted 3y ago by Guilherme Costa‭  ·  closed 3y ago by Peter Taylor‭

skewness statistics
33%
+0 −2
Why 1. multiply the number of independent options? 2. add the number of exclusive options?

3 answers  ·  posted 3y ago by DNB‭  ·  last activity 3y ago by Tim Pederick‭

probability
71%
+3 −0
Maximize Independent Variable of Matrix Multiplication

1 answer  ·  posted 3y ago by Josh Hyatt‭  ·  edited 3y ago by Josh Hyatt‭

matrices vector
75%
+4 −0
Is it impossible to prove Jensen's inequality by way of step functions?

1 answer  ·  posted 3y ago by whybecause‭  ·  last activity 3y ago by whybecause‭

real-analysis convex-analysis Jensen's-inequality
71%
+3 −0
"Pointwise equicontinuity implies uniform" implies compact

1 answer  ·  posted 3y ago by whybecause‭  ·  last activity 3y ago by whybecause‭

real-analysis equicontinuity continuity metric-spaces
33%
+0 −2
How to intuit, construe multiplicands and multiplicators $\le 10$ resulting from $\dbinom pc$, WITHOUT division or factorials? [duplicate]

0 answers  ·  posted 3y ago by DNB‭  ·  edited 3y ago by DNB‭

combinatorics
60%
+1 −0
$\{f_n\}\to f$ in $X$ implies $||f||\le\liminf||f_n||$

1 answer  ·  posted 3y ago by whybecause‭  ·  last activity 3y ago by whybecause‭

real-analysis functionals normed-vector-space
75%
+4 −0
Missing a solution: Are A and B always equal if A-B=0

3 answers  ·  posted 3y ago by re89j‭  ·  last activity 3y ago by tommi‭

logic equation algebra problem
33%
+0 −2
Out of 4 people, why does ways to choose a 2-person committee overcount by 2 the ways to divide the 4 into 2 teams of 2?

1 answer  ·  posted 4y ago by DNB‭  ·  last activity 3y ago by Tim Pederick‭

probability
33%
+1 −4
How can you "easily see that such squares [of side length $\sqrt{13}$ and $\sqrt{18}$] will not fit into the [4 × 4] grid"?

1 answer  ·  posted 3y ago by DNB‭  ·  last activity 3y ago by Tim Pederick‭

geometry
40%
+0 −1
How can a 15 year old construe the LHS of Generalized Vandermonde's Identity, when it lacks summation limits and a summation index?

2 answers  ·  posted 3y ago by DNB‭  ·  last activity 3y ago by r~~‭

summation
40%
+0 −1
To correct for overcounting, why can't we divide by the sum of the over-counts? [duplicate]

0 answers  ·  posted 3y ago by DNB‭  ·  closed as duplicate 3y ago by Peter Taylor‭

combinatorics
33%
+0 −2
Why's Pr(the running total of a fair dice rolled repeatedly = n) = $\frac16 (p_{n-1} + p_{n-2} + p_{n-3} + p_{n-4} + p_{n-5} + p_{n-6})$?

0 answers  ·  posted 3y ago by DNB‭  ·  edited 3y ago by DNB‭

probability
40%
+0 −1
Why's a 2-player game with "win by two" rule = Gambler's Ruin where each player starts with $2? Why N = 4?

0 answers  ·  posted 3y ago by DNB‭  ·  edited 3y ago by DNB‭

probability
60%
+1 −0
How's it possible to arrange 0 objects? How can 0! = 1?

3 answers  ·  posted 3y ago by DNB‭  ·  edited 3y ago by Quintec‭

combinatorics
40%
+0 −1
If C = Calvin wins the match, and $X \thicksim Bin(2, p) =$ how many of the first 2 games he wins — then why P(C|X = 1) = P(C)?

1 answer  ·  posted 3y ago by DNB‭  ·  last activity 3y ago by Peter Taylor‭

probability
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