105,233 reputation
694191
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 ...


Jul
3
comment If $V$ is a vector space over $\mathbb{Q}$ and $\alpha \in \mathrm{End}(V)$ is a projection, show that $\mathrm{spec}(\alpha)\subseteq {0,1}$
For a proof that $\operatorname{spec}(\alpha)\in\{0,1\}$, you can hardly suppose in the beginning that $\operatorname{spec}(\alpha)\in\{0,1\}$.
Jul
3
answered how to prove Exponential is strictly positive?
Jul
3
revised No. of ways to arrange 4R and 3L so that there is exactly 4 times change from L to R or R to L.
added 244 characters in body
Jul
3
answered No. of ways to arrange 4R and 3L so that there is exactly 4 times change from L to R or R to L.
Jul
3
answered Entire functions that satisfy certain equation.
Jul
3
comment Showing $ x-y\in\mathbb{Q}$ is an equivalence relation?
If you look at thecorrect answers more closely, you may notice that the proofes hinge on the fact that $\mathbb Q$ is a subgroup of $\mathbb R$ (under addition): You make use of the neutral element for reflexivity, of inverses for symmetry and of closedness under addition for transitivity.
Jul
3
comment What does $\mathbb{R}^J$ mean?
@Actually, you should take $J=\{0,\ldots,n-1\}$ or $\{1,\ldots,n\}$. A function from an $n$-element set is just a list (of length $n$) of values, so not much different from an $n$-tuple. The cardinality of $\mathbb R^n$ happens to be the same as that of $\mathbb R$, but that is not the main point - the finite case is the motivation only.
Jul
3
answered What does $\mathbb{R}^J$ mean?
Jul
3
revised Factor n=59305397 given that $ p-q \le 10 $
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Jul
3
answered Factor n=59305397 given that $ p-q \le 10 $
Jul
3
answered Convergent $\{a_n\}$ $\nRightarrow$ convergent $\{\frac{a_{n+1}}{a_n}\}$
Jul
3
comment How many order relations there are on $A=\{1,2,3 \}$
Yes, non elements comparable means that the realtion is empty. We can have $1>3$ because the orders we want to enumerate are not required to be sub-orders of the natural order.
Jul
3
comment Decomposing an element into product of elements of finite order
So you may go back to square one with $SL_2(\mathbb R)$ :)
Jul
3
answered Greatest value of the binomial coefficient.
Jul
3
answered How many order relations there are on $A=\{1,2,3 \}$
Jul
3
comment What kind of rings have exactly three ideals?
Not much more generally, let $R$ be a local ring with (unique) maximal ideal $\mathfrak m$. Then $R/\mathfrak m^2$ has exactly three ideals. And each ring with exactly three ideals can be obtained this way.
Jul
3
comment Ordered rings $R$ with $ab = ba$, $ab \leq ba$ or $ba \leq ab$ for all $a, b \in R$?
You mean $\forall a,b\in R\colon ab\le ba$? Well, then $R$ is necessarily commutative because $ab\le ba\le ab$ implies $ab=ba$.
Jul
3
comment Find formula OR Impose Condition
There exists a circle such that ...
Jul
3
answered Use of prime symbol in proof writing
Jul
3
revised Find all the functions $f:\mathbb{R}→\mathbb{R}$ such that $f(mx+c)=mf(x)+c$
added 22 characters in body