User Michael Seifert - Mathematics Stack Exchange

45 votes

Do $3/8$ (37.5%) of Quadratics Have No $x$-Intercepts?

answered Jul 29, 2019 at 20:37

18 votes

Accepted

Clay Institute Navier Stokes Part 2

answered Aug 15, 2017 at 14:47

16 votes

What's a fair way to share fees in a group road trip with a personal and a rental car?

answered Jul 2, 2020 at 19:55

16 votes

$f : [0,\infty) → \mathbb{R}$ with $f(0) = f'(0) = 0$ and $f(x) < x^2$ and $f',f'',f''' > 0$?

answered Jan 17, 2019 at 20:38

16 votes

Accepted

Can a function be differentiable if the limit does not exist?

answered Mar 28, 2022 at 17:16

15 votes

Is the arc length always irrational between two rational points?

answered Jul 11, 2019 at 20:13

15 votes

Accepted

The functional equation $f(x+x) = f(x)f(x)$

answered Sep 27, 2016 at 14:07

12 votes

Is $(p-1)!+p$ a prime for every prime $p$?

answered Jan 29, 2016 at 17:44

12 votes

Accepted

Unknown syntax with multiplication?

answered Apr 30, 2017 at 14:36

12 votes

Walking around a cube to return to starting point

answered Aug 22, 2023 at 2:16

11 votes

Accepted

Is there a Lagrangian that produces these equations? How can I find one if it exists?

answered Dec 21, 2021 at 21:54

9 votes

Accepted

Why the substitution is not working even though its bijective?

answered Mar 14, 2021 at 23:51

8 votes

Accepted

Is this a valid convergence test (for sequences)?

answered Aug 23, 2018 at 21:51

8 votes

Is it possible to convert a linear system in an ODE of higher order

answered Jun 6, 2017 at 20:00

8 votes

What is the average number of draws (2 cards per draw with shuffles in between) before I had seen all 52 cards in the deck?

answered Aug 21, 2015 at 19:40

8 votes

Accepted

Choose $a, b$ so that $\cos(x) - \frac{1+ax^2}{1+bx^2}$ would be as infinitely small as possible on ${x \to 0}$ using Taylor polynomial

answered Dec 24, 2016 at 18:06

7 votes

Accepted

How to prove an ordinary differential equation is not separable?

answered Mar 21, 2017 at 13:35

7 votes

Accepted

PDF of uniform distribution over the hypersphere and the hyperball

answered May 10, 2017 at 22:44

6 votes

Coloring of $\mathbb{R}^3$ into 3 colors

answered Nov 17, 2017 at 21:01

6 votes

Counting the Number of Real Roots of $y^{3}-3y+1$

answered Mar 13, 2017 at 19:26

6 votes

Is curl of a given vector always perpendicular to the given vector field?

answered Dec 27, 2016 at 13:19

6 votes

Is this contraction of metric tensor derivatives symmetric?

answered Jun 30, 2016 at 14:43

6 votes

If $A$, $B$ idempotent and $AB=0$, then $A+B$ idempotent.

answered Apr 27, 2021 at 14:19

6 votes

How to calculate the dimensions of the required 20 regular hexagons and 12 regular pentagons for a sphere of given diameter (the soccer ball issue)

answered Sep 19, 2021 at 14:09

5 votes

Accepted

Feynman Lectures p264: How does $r^2 = \rho^2 + a^2$ imply $\rho\, {\rm d}\rho = r\, {\rm d}r$

answered Sep 2, 2021 at 14:40

5 votes

Accepted

Find the determinant of a particular matrix without a calculator.

answered Aug 24, 2021 at 1:50

5 votes

Accepted

What are the eigenvectors of this matrix and if these are the eigenvectors, why aren't they orthogonal?

answered Dec 21, 2021 at 22:29

5 votes

Accepted

Can you list me all the geometrical conditions of two ellipses with a common focus?

answered Mar 10, 2022 at 16:50

5 votes

Accepted

Asymptotics for ODE with no closed form solution

answered Feb 7, 2018 at 14:12

5 votes

Accepted

Wanted: metric in which the volume of euclidean space is finite

answered Jul 22, 2019 at 14:47

Stack Exchange Network

288 Answers

Do $3/8$ (37.5%) of Quadratics Have No $x$-Intercepts?

Clay Institute Navier Stokes Part 2

What's a fair way to share fees in a group road trip with a personal and a rental car?

$f : [0,\infty) → \mathbb{R}$ with $f(0) = f'(0) = 0$ and $f(x) < x^2$ and $f',f'',f''' > 0$?

Can a function be differentiable if the limit does not exist?

Is the arc length always irrational between two rational points?

The functional equation $f(x+x) = f(x)f(x)$

Is $(p-1)!+p$ a prime for every prime $p$?

Unknown syntax with multiplication?

Walking around a cube to return to starting point

Is there a Lagrangian that produces these equations? How can I find one if it exists?

Why the substitution is not working even though its bijective?

Is this a valid convergence test (for sequences)?

Is it possible to convert a linear system in an ODE of higher order

What is the average number of draws (2 cards per draw with shuffles in between) before I had seen all 52 cards in the deck?

Choose $a, b$ so that $\cos(x) - \frac{1+ax^2}{1+bx^2}$ would be as infinitely small as possible on ${x \to 0}$ using Taylor polynomial

How to prove an ordinary differential equation is not separable?

PDF of uniform distribution over the hypersphere and the hyperball

Coloring of $\mathbb{R}^3$ into 3 colors

Counting the Number of Real Roots of $y^{3}-3y+1$

Is curl of a given vector always perpendicular to the given vector field?

Is this contraction of metric tensor derivatives symmetric?

If $A$, $B$ idempotent and $AB=0$, then $A+B$ idempotent.

How to calculate the dimensions of the required 20 regular hexagons and 12 regular pentagons for a sphere of given diameter (the soccer ball issue)

Feynman Lectures p264: How does $r^2 = \rho^2 + a^2$ imply $\rho\, {\rm d}\rho = r\, {\rm d}r$

Find the determinant of a particular matrix without a calculator.

What are the eigenvectors of this matrix and if these are the eigenvectors, why aren't they orthogonal?

Can you list me all the geometrical conditions of two ellipses with a common focus?

Asymptotics for ODE with no closed form solution

Wanted: metric in which the volume of euclidean space is finite