User MR_BD

57 votes

Accepted

How can I easily double any size number in my head?

answered Dec 27, 2016 at 15:55

41 votes

Visually stunning math concepts which are easy to explain

answered Jan 2, 2017 at 16:37

17 votes

How to explain to my daughter that $\frac {2}{3}$ is greater than $\frac {3}{5}$?

answered Apr 13, 2017 at 18:55

14 votes

Accepted

Sum of roots of any equation

answered Apr 8, 2017 at 8:51

11 votes

Why doesn't the limit of $\frac{e^{\frac1x}-1}{e^{\frac1x}+1}$ exist?

answered Apr 13, 2017 at 17:22

9 votes

Is it possible that two independent variables become dependent conditioning on a third random variable

answered Aug 22, 2016 at 20:10

9 votes

Accepted

Is $\prod_{p}{\frac{p-1}{p+1}}=0$?

answered Mar 22, 2017 at 21:19

7 votes

List of interesting math videos / documentaries

answered Apr 6, 2017 at 7:45

7 votes

A proof of Young's inequality

answered Apr 13, 2017 at 18:18

6 votes

Trace inequality on the product of positive semi-definite matrices

answered Jan 26, 2017 at 13:03

6 votes

Accepted

If an element is not in the set difference $A\setminus B \: \:?$

answered Feb 13, 2017 at 7:59

5 votes

Accepted

What's the probability of tossing $r$ heads in a row before $s$ tails in a row?

answered Aug 2, 2016 at 15:14

4 votes

Sine and Cosine Derivatives

answered Aug 22, 2016 at 20:23

4 votes

Accepted

Which trigonometric function to use?

answered Apr 8, 2017 at 14:58

4 votes

Accepted

Show that two sides of a triangle are perpendicular

answered Apr 8, 2017 at 18:29

4 votes

If given $P(B\mid A) =4/5$, $P(B\mid A^\complement)= 2/5$ and $P(B)= 1/2$, what is the probability of $A$?

answered Aug 11, 2019 at 16:26

3 votes

Is this remark about random graph easy to prove?

answered Apr 7, 2017 at 9:02

3 votes

Accepted

If $X \sim X^2$, then $X$ is independent of itself?

answered Apr 11, 2017 at 11:26

3 votes

Constructive proof for $p|x^2+1$

answered Mar 25, 2017 at 11:07

3 votes

Do all mathematical ideas eventually find their way into the real world?

answered Feb 3, 2017 at 13:43

2 votes

$X$ and $Y$ are $i.i.d.$ random variables belonging to uniform distribution. Find probability of $Y$ less than a function of $X$

answered Feb 3, 2017 at 12:44

2 votes

How many distinct four-digit integers can one make from the digits $1,3,3,7,7,8$?

answered Mar 23, 2017 at 8:46

2 votes

Accepted

What does $R \rightarrow R$ means in functions?

answered Feb 26, 2015 at 15:36

2 votes

Liouville function and perfect square

answered Jul 19, 2016 at 17:13

2 votes

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

answered Feb 12, 2017 at 7:03

2 votes

Prove that the polynomial $f_n(x)=nx^{n+1}-(n+1)x^n+1$ is divisible by $(x-1)^2$

answered Jan 1, 2017 at 19:41

2 votes

If $(f,g) \in R$ then $( (f \circ f),(g \circ g) )\in R$

answered Sep 22, 2022 at 22:45

2 votes

PMF for the maximum of two four-sided dices

answered Aug 18, 2019 at 13:04

2 votes

Motivation for the Basel problem

answered Aug 5, 2018 at 12:57

1 vote

Some good book suggestions beyond linear algebra?

answered Aug 6, 2018 at 15:52

Stack Exchange Network

64 Answers

How can I easily double any size number in my head?

Visually stunning math concepts which are easy to explain

How to explain to my daughter that $\frac {2}{3}$ is greater than $\frac {3}{5}$?

Sum of roots of any equation

Why doesn't the limit of $\frac{e^{\frac1x}-1}{e^{\frac1x}+1}$ exist?

Is it possible that two independent variables become dependent conditioning on a third random variable

Is $\prod_{p}{\frac{p-1}{p+1}}=0$?

List of interesting math videos / documentaries

A proof of Young's inequality

Trace inequality on the product of positive semi-definite matrices

If an element is not in the set difference $A\setminus B \: \:?$

What's the probability of tossing $r$ heads in a row before $s$ tails in a row?

Sine and Cosine Derivatives

Which trigonometric function to use?

Show that two sides of a triangle are perpendicular

If given $P(B\mid A) =4/5$, $P(B\mid A^\complement)= 2/5$ and $P(B)= 1/2$, what is the probability of $A$?

Is this remark about random graph easy to prove?

If $X \sim X^2$, then $X$ is independent of itself?

Constructive proof for $p|x^2+1$

Do all mathematical ideas eventually find their way into the real world?

$X$ and $Y$ are $i.i.d.$ random variables belonging to uniform distribution. Find probability of $Y$ less than a function of $X$

How many distinct four-digit integers can one make from the digits $1,3,3,7,7,8$?

What does $R \rightarrow R$ means in functions?

Liouville function and perfect square

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

Prove that the polynomial $f_n(x)=nx^{n+1}-(n+1)x^n+1$ is divisible by $(x-1)^2$

If $(f,g) \in R$ then $( (f \circ f),(g \circ g) )\in R$

PMF for the maximum of two four-sided dices

Motivation for the Basel problem

Some good book suggestions beyond linear algebra?