106,269 reputation
696194
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 48
visits member for 1 year, 10 months
seen yesterday

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


Sep
13
answered Show $g(x)=\sqrt{x}$ is continuous at x=4
Sep
13
answered Proving basic limit laws without finding $\delta$s.
Sep
13
answered Solution to $x^2+x-1\equiv 0$ mod $p$
Sep
12
answered Let $A$ be an $m\times n$ matrix. If $\forall \vec{x}\in\mathbb{R}^{n},\ A\vec{x}=\vec{0}$, show that $A$ is the zero matrix.
Sep
12
comment Infinite composition of automorphisms.
The answerd given so far give examples where the limit can hardly be defined or where the limit (according to pointwise convergence) exists but fails to be an automorphism. Are there also examples where the limit exists, but is not even a homomorphism?
Sep
12
answered How can I compute a similarity score between two documents with the provided algorithm?
Sep
12
comment An inconstructible quadrilateral
Why does this triangle have four vertices?
Sep
11
comment Is the following equivalent to the axiom of choice?
@AsafKaragila Well, not really. If we $|\emptyset|\le^*|B|$ is false by the simplified definition, then the case $A=\emptyset$ is trivially true, and that does not hurt. All this $\le, \le^*$ is just fancy writing for "If there exists a surjection $B\to A$, there exists an injection $A\to B$".
Sep
11
answered Roll five dice. What's the chance of rolling exactly one pair?
Sep
11
comment Computing sums of divisors in $O(\sqrt n)$ time?
@sudeepdino008 At least we can verify that (if $n$ is not a square) $p(n)-p(n-1)=2\sum (\lfloor\frac nk\rfloor - \lfloor \frac {n-1}k\rfloor) = 2\sum_{d|n, d^2<n}1$ as required. And if $n=m^2$ is a square, the additional summand $2m$ is correctly compensated by $m^2-(m-1)^2=2m-1$.
Sep
11
answered Prove that an uncountable set X is equivalent to X\Y where Y is a denumerable subset of X
Sep
11
comment Small symbols behind parantheses
Would something like $(n)_k=\frac{(n+k-1)!}{(n-1)!}$ make sense?
Sep
11
answered Combinatorical proof $\sum_{k=0}^n{{2n+1}\choose k}=2^{2n}$
Sep
11
answered A postive, decreasing function $f$ such that $\lim_{n \rightarrow \infty} \ln f(n) / \ln n$ neither diverges nor converges to $-\infty$.
Sep
11
comment A postive, decreasing function $f$ such that $\lim_{n \rightarrow \infty} \ln f(n) / \ln n$ neither diverges nor converges to $-\infty$.
But $\ln f(n)$ need not be bounded!
Sep
11
answered how to defined subset of highest n values from a set
Sep
11
awarded  inequality
Sep
10
awarded  Good Answer
Sep
10
answered Bijection between $\mathbb{R} \times \mathbb{R}$ and $\mathbb{R}$
Sep
10
answered Proving that 4 specified sets are not algebraic