110,128 reputation
6101200
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 48
visits member for 2 years
seen 2 hours ago

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


Oct
17
answered The sequence of prime gaps is never strictly monotonic
Oct
17
answered $|3^a-2^b|\neq p$, from a contest
Oct
17
comment $|3^a-2^b|\neq p$, from a contest
@Oleg567 Now remains to be seen elementary/at contest level that $41$ cannot be written as $|3^a-2^b|$ ...
Oct
17
answered How many paths are there from A to B?
Oct
17
comment proof that the three interior angles of a triangle is congruent to a straight line (without measurements)
What's the use of 7? You had that in 5 already.
Oct
17
answered Covering a chess board with $2$ missing places with $31$ dominoes
Oct
17
comment Covering a chess board with $2$ missing places with $31$ dominoes
Naively, the method might end with the gaps in the last row in an impossible position.
Oct
17
comment About the proof of Nullstellensatz
@bateman Injectivity is trivial as fields lack ideals.
Oct
17
comment About the proof of Nullstellensatz
@martini Well, I think one hsould simply note that $\phi$ is the identity on $k$. (A priori, it might be that $k$ is isomorphic to a subfield of itself)
Oct
16
answered What restrictions are on th sum of two fourth powers?
Oct
16
answered Is this symbolic expression correct?
Oct
16
answered If a sequences has two subsequenceswhich converge to to different limits then the sequence cannot be converging
Oct
16
answered A question from GRE math sub 9367, problem 59
Oct
16
comment Probability question
+1 for the brief and yet selfexplanatory distinction lost vs "lost".
Oct
16
comment What's the criteria for swapping the order of floor and limit?
However, we do have $$\left\lfloor \lim_{n\to\infty} a_n\right\rfloor = \lim_{n\to \infty}\lfloor a_n\rfloor$$ if $\lim_{n\to\infty} a_n\notin\mathbb Z$ or $a_n$ is eventually non-increasing.
Oct
16
answered Integrals Regulated functions
Oct
16
comment Is the set $\{0,1\}$ opened or closed?
As a subset of $\mathbb R$ (with standard topology), $\{0,1\}$ is closed and not open, has no interior points, hence is its own boundary.
Oct
16
comment How would I go about writing this proof in a formal way?
If you still have doubts and think it necesary to plug in odd numbers for $c$ and look out for counterexamples, you do not have a trustworthy proof yet. Moreover, if you plug in odd values for testing, you do not do the testing right. Finally, $c=1$ gives you problems as $c^2+7=2n$ implies $n=4$ whereas $c=2n+1$ implies $n=0$ - you cannot have $n=4$ and $n=0$ at the same time.
Oct
16
reviewed Close How prove this inequality: $\sum_{i,j=1}^{n}|x_{i}+x_{j}|\ge n\sum_{i=1}^{n}|x_{i}|$?
Oct
16
reviewed Close Is the quadratic formula a complete formular for solving the quadratic equation?