128,158 reputation
9121250
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 49
visits member for 2 years, 5 months
seen 2 hours ago

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


Jan
26
comment Are $121$ and $400$ the only perfect squares of the form $\sum\limits_{k=0}^{n}p^k$?
$p$ an integer or $p$ a prime?
Jan
26
comment $f : ]0, \infty[\to\mathbb{R}$ Prove that $\lim_{x\to\infty} f(x) = 0$ if $\lim_{x\to\infty} [f(x)+f'(x)] = 0$
@DavidMitra That (or the knowledge thereof) may depend on the literature used. For example, some only encyclopedia requires for $\frac{f(x)}{g(x)}$ that either $\lim f(x)=\lim g(x)=0$ or $\lim|f(x)|=\lim |g(x)|=\infty$ ...
Jan
26
comment $f : ]0, \infty[\to\mathbb{R}$ Prove that $\lim_{x\to\infty} f(x) = 0$ if $\lim_{x\to\infty} [f(x)+f'(x)] = 0$
Problem is: Are we allowed in the first place to apply l'Hopital? Of course $e^x\to \infty$, but $f(x)e^x$ might a priori oscillate between $0$ and $\infty$.
Jan
25
comment Does the dot product angle formula work for $\Bbb{R}^n$?
Actually, this is used as the definition of angle in higher $n$
Jan
25
revised prove by mathematical induction
added 24 characters in body
Jan
25
awarded  Nice Answer
Jan
25
answered If $f(n)$ is not $\Theta (g(n))$ does it follow that $\log f(n)$ is not $\Theta(\log g(n))$?
Jan
25
comment Is there a subset of natural numbers with a special property
What about $A=\mathbb N\setminus\{1\}$?
Jan
25
answered Number of zeros of $ f^n $
Jan
25
answered Difficulty in finding a counterexample
Jan
25
answered Identify encryption scheme - possibly DSA or Diffie Hellman - only client shares key
Jan
25
awarded  diophantine-equations
Jan
24
awarded  Enlightened
Jan
24
answered How to prove the closure $\bigcup_{n\ge 1} F_{n}$ is totally bounded and closed
Jan
24
awarded  Guru
Jan
24
comment Can somebody explain with one example the concepts: Lemma-Hypothesis-Theorem-Assumption-Proof-Axiom-Thesis-Determination-Definition-Proof
The differenc between lemma, theorem (and many others, such as proposiiton, claim, corollary) is only in the eye of the beholder. - Maybe the same could sometimes be said about hypothesis, assumption, axiom.
Jan
24
answered Let $F$ be a class of sets. Prove that $B - \mathop{\bigcup}_{A\in F} A = \mathop{\bigcap}_{A\in F} (B-A)$
Jan
24
comment Let $F$ be a class of sets. Prove that $B - \mathop{\bigcup}_{A\in F} A = \mathop{\bigcap}_{A\in F} (B-A)$
The claim sounds wrong if $F$ is the empty class
Jan
24
comment What computations would advance math knowledge a lot?
How does "just for one day" put any restriction on "capable of computing anything"?
Jan
24
comment Why does $\sqrt{x} / y =\sqrt{x/y/y}$?
One caveat: The eaquality does not hold with negative $y$.