108,630 reputation
698199
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 48
visits member for 1 year, 11 months
seen 1 hour ago

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


Aug
12
comment Proving that 0 * x = 0 using only first order logic
The equation holds if $*$ denotes the multiplication in a ring where $0$ is the additive neutral element (and $x$ an arbitary element. So look up ring axioms.
Aug
12
comment ZFC and apples described using only fundamental axioms (complete expanded reasoning)
You may be interested in working through Russel and Whitehead, Pricipia Mathematica, where you will find your equation ("a sometimes useful result") proved on page 378
Aug
12
answered A question regarding irrational lengths in reality
Aug
12
comment Limit of $ (2^n)\sin(n) $ as $n$ goes to infinity
Questions should be be marked as solved by editing the title, but rather by accepting an answer. (Admittedly, David Mitra's comment may be more informative than Graham Kemp's answer)
Aug
12
answered What is the radius of a planet, given some basic information?
Aug
12
awarded  continuity
Aug
11
answered Proof of an equality involving $\phi(n)$
Aug
11
revised Proof of an equality involving $\phi(n)$
added 3 characters in body
Aug
11
revised Uniqueness proof for a certain functional equation
added 33 characters in body
Aug
11
answered Uniqueness proof for a certain functional equation
Aug
11
comment $G$ is non-abelian and satisfies $(ab)^2=(ba)^2 , \forall a,b \in G$
$D_4\oplus \mathbb Z$ is infinite
Aug
11
comment Let $G$ be a group of order 30. Show that $G$ has a subgroup of order 15.
CAn you fins out how many Sylow groups there are for each prime?
Aug
11
answered Extending a homeomorphism of the open disk to the boundary.
Aug
11
comment Simple subtraction that I can't figure out.
I the ball cost 10p, the bat would cost 1£ more, i.e. £1.10 and both items togetrhre would cost £1.20, not £1.10.
Aug
11
answered $G$ is non-abelian and satisfies $(ab)^2=(ba)^2 , \forall a,b \in G$
Aug
11
comment Looking for a proof that the diameter of the smallest bounding circle is less than or equal to $\frac{2}{\sqrt{3}}$ times the diameter of the set
You mean $ p,q\in E$ in the definition of diam.
Aug
11
answered What's the probability of third coin being of 50 cent?
Aug
10
answered How to solve the recurrence relation $T(n) = T(\lceil n/2\rceil) + T(\lfloor n/2\rfloor) + 2$
Aug
10
comment How to solve the recurrence relation $T(n) = T(\lceil n/2\rceil) + T(\lfloor n/2\rfloor) + 2$
A strange observation: $T(n)$ is odd iff the binary expansion of $n$ is of the form $11***1$ (provided $n>3$)
Aug
10
comment Is $\{(x,y,z,0)\in\mathbb{R}^4:x^4+y^2+z^2=1\}$ diffeomorphic to $S^2$?
Try with partial maps. For the part where $|x|<1$, both your set and $S^2$ are diffeomorphic to a cyclinder via $(x,y,z)\mapsto (\frac{y}{\sqrt{y^2+z^2}},\frac{z}{\sqrt{y^2+z^2}}$. And for $x>0$ as well as $x<0$ your maps are smooth. Finally, where the maps of this atlas overlap, the transitions are smoot.