123,711 reputation
8117240
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 49
visits member for 2 years, 3 months
seen 6 hours ago

I did study math and had a knack for it, but I am sooo out of that business now ...


Dec
13
comment To prove that $ \lim_{x\to 0^-} \frac{1}{x} = -\infty$, how do we choose $\delta$?
It's hard to tell because $\lim_{x\to-\infty}\frac1x\ne -\infty$.
Dec
13
comment How to prove that if R is a partial order then also $R^{-1}$ is also a partial order?
You may want to be encouranging, but especially the OP proof of antisymmetry is not what I would call basically correct
Dec
13
comment How to prove that if R is a partial order then also $R^{-1}$ is also a partial order?
Your proof suffers from you not starting with the appropriate premises for what you want to show. Cf. user105103's answer: To show that "If A then B" holds for $R^{-1}$, start by assuming that A holds for $R^{-1}$, translate what that means for $R$, use the properties of $R$ to show something else about $R$, which hopefully translates into property B of $R^{-1}$.
Dec
13
comment can anyone prove this with induction?
Well, maybe the correct answer is "No" for some :)
Dec
13
comment isomorphism and circle group
I edited the LaTeX a bit, but may have messed it up. Did you mean (as second factor of the proeduct) the multiplicative group of positive reals or the additive group of reals? (Not that it matters a lot)
Dec
13
revised isomorphism and circle group
added 16 characters in body
Dec
13
comment If $f(x)=f(\delta x), \delta>0$ a.e then $f$ is constant?
And $\delta=1$ is probably excluded ;)
Dec
13
answered How prove each $k$ there exits infinite set of numbers $n$, are divisible by $m$
Dec
13
revised How prove each $k$ there exits infinite set of numbers $n$, are divisible by $m$
added 5 characters in body; edited title
Dec
13
comment If $f(x)=f(\delta x), \delta>0$ a.e then $f$ is constant?
For almostall $x$? For almost all $\delta$? For almost all delta for almost all $x$? For some $\delta$ for almost all $x$?
Dec
12
comment Cauchy sequence in metric space
@AWertheim It is Cauchy because it converges to $\sqrt 2$. Indeed, the $N$th term differs by less than $\frac1N$ from the limit, and hence by less than $\frac2N$ from any later term.
Dec
12
revised show that there exist an element $g$ of a group $G$ such that $g^q$ is in $H$
added 23 characters in body; edited title
Dec
12
comment show that there exist an element $g$ of a group $G$ such that $g^q$ is in $H$
As it stands, the result is trivial - just pick any $g\in H$, or even $g=1$. I assume you want $g$ to be an element of $G$ that is not in $H$.
Dec
12
revised Help with Random High Card Probability Question
added 115 characters in body
Dec
12
comment Can anyone give an example for this theorem related to planar graphs?
I didn't say there was anything needing a fix :) - "... equals $2q$" is true with suitable counting. E.g., in the star graoh with $e$ edges, the region may be viewed as a degenerate $2n$-gon.
Dec
12
comment Can anyone give an example for this theorem related to planar graphs?
In other words, by reading the proof carefully we note that "each region has degree $3$ or more" is the reason for the inequality.
Dec
12
answered Constructing a random sampler from a random coin (algorithm)
Dec
12
revised Construct quadrangle with given angles and perpendicular diagonals
added 109 characters in body
Dec
12
revised Construct quadrangle with given angles and perpendicular diagonals
added 49 characters in body
Dec
12
comment Construct quadrangle with given angles and perpendicular diagonals
@abel not with success