120,738 reputation
7112230
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 48
visits member for 2 years, 2 months
seen 30 mins ago

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


Nov
21
answered $\mathbb{Q} \simeq \mathbb{Q}^*_+$ isomorphism
Nov
21
answered Multiple choice question on continuous function on a unit ball
Nov
21
comment Prove that any subfield of $\Bbb R$ contains $\Bbb Q$
In priciple Yes, though you may want to elaborate by which method one can conclude from $1\in F$ that $\mathbb Z\subseteq F$ and by which method one can conclude from this that $\mathbb Q\subseteq F$. (as in: Why is your proof better than "$1\in F$, hence $\mathbb Q\subseteq F$"?)
Nov
21
comment Need help understanding this proof that if $H=\{e, (1 \, 2)(3 \, 4), (1\, 3)(2 \, 4), (1 \, 4)(2\, 3)\}$, then it is a normal subgroup of $S_4$.
Maybe simpler: conjugate elements of $S_n$ have the same cycle type. Your $H$ contains all elements of $S_4$ that have cycle type $(a\;b)(c\;d)$.
Nov
21
answered Maximum GCD of two polynomials
Nov
21
answered Find an example on a sequence of real-valued functions $(f_n(x))_{n\in\mathbb{N}}$ satisfying the given conditions
Nov
21
comment Explanation of Proof that field sum of more than 2 elements is 0.
I greatly enlarged the word count in the original answer - hope that helps.
Nov
21
revised The sum of the elements in a field of at least three elements is 0
added 1409 characters in body
Nov
21
revised The sum of the elements in a field of at least three elements is 0
deleted 1 character in body
Nov
21
comment What are numbers with E in them called?
looks like IEEE floating point to me ...
Nov
21
comment Modular exponentiation twice over
In the non-coprime case, additionally use the Chinese Remainder Thorem, and usually the exponent of any commmon prime factor of $a$ and $m$ will occur in $a^b$ in trivially much higher power than in $m$.
Nov
21
awarded  Enlightened
Nov
21
comment Equivalence of these two definitions of limit at a given point
In definition 1, don't you want to impose a special property that $F$ has at $c$? Also, what did you introduce $\delta$ for in the first sentence?
Nov
21
comment Divergence or convergence of alternating series
Yes, I do agree
Nov
21
answered Continuity of vector space operations in a normed space
Nov
21
comment Continuity of vector space operations in a normed space
What's your math question? Be specific. Also in the title
Nov
21
comment A mathematical statement is logically equivalent to a related statement
Or: Reformulation with different variable names ...
Nov
20
comment determining the cardinality
$C$ is also $\subset \mathcal P(\mathbb R)$, so $C\subset S$ does not settle the question of cardinality completely.
Nov
20
answered determining the cardinality
Nov
20
answered Prove that the following set is dense in R