114,399 reputation
7106211
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 48
visits member for 2 years, 1 month
seen 8 mins ago

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


Dec
2
comment Unknown maths topic, does the numbers hold
Is it safe to click that link?
Dec
2
answered Is it necessary to use the axiom of Regularity to prove the successor function being injective?
Dec
2
comment Is it necessary to use the axiom of Regularity to prove the successor function being injective?
@AndresCaicedo Well, as you need to say "since", it is a (very shallow) theorem.
Dec
2
comment Is it necessary to use the axiom of Regularity to prove the successor function being injective?
@AndresCaicedo I prefer to say that on ordinals regularity is a theorem, not an axiom.
Dec
2
revised Limit $\lim_{n\to\infty}n\frac{\sin\frac{1}{n}-\frac{1}{n}}{1+\frac{1}{n}}$
edited body
Dec
2
comment Circle containing three points, maybe all collinear
"when at least two of the are collinear"? Two points are always collinear, three points are always coplanar. The exceptional case is when all three points are collinear (which includes as special case that some points may coincide)
Dec
2
answered Context free grammar question
Dec
2
answered Maximum of |sin x| + |sin y| + |sin z|
Dec
2
awarded  Nice Answer
Dec
2
answered What steps should I be doing to determine if this series is convergent or divergent?
Dec
1
reviewed No Action Needed Does $E^2 \; ( E \approx 1.2640847\ldots)$ equal $D \approx 1.5979102\ldots$?
Dec
1
comment Show that $\sum _{k=1}^\infty (1-\frac{x_{k+1}}{x_k})$ converges iff $(x_k)_k$ is bounded.
If $x_k\to a\ne0$ then $1+\frac{x_{k+1}}{x_k}\to 2$, I'm afraid. Also, $\frac{x_{k+1}}{x_k}\to 1$ does not implie $x_k$ is bounded: consider $x_k=k$.
Dec
1
comment Does “locally connected and path-connected” imply locally path-connected?
Was "Counterexamples in topology" among the sevreral boos?
Dec
1
answered the product of topological spaces is compact, then each of its factors is compact.
Dec
1
comment Does the sequence $A_n = \frac{\sin (n)}{\sqrt{n}}$ converge to $0$?
No l'Hospital, just $|A_n|\le \frac 1{\sqrt n}$ should be enough
Dec
1
comment Proper subset of span of only one vector
Don't use induction. Note that $\subseteq$ is clear and what can you conclude from $v_j\in\operatorname{span}$?
Dec
1
comment Proving that the ring $R$ of $2\times 2$ matrices over $\Bbb{Q}$ contains only two ideals: $(0)$ and $R$.
Long story short, the ideal generated by $a$ is not $aR$.
Dec
1
reviewed Leave Open Use I as an variable in Maple
Dec
1
reviewed Close How many positive integers less than 1000 are divisible
Dec
1
answered cardinality of a set of natural lattice points versus natural numbers