108,765 reputation
698199
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 48
visits member for 1 year, 11 months
seen 17 mins ago

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


Oct
14
answered On the definition of product of groups
Oct
14
comment Find the pattern - puzzle
This also seems to be the overwhelming majority opinion if one googles 151872
Oct
14
reviewed Reject suggested edit on If the product of two numbers is positive and less than one, what can I conclude about the quotient?
Oct
14
reviewed Approve suggested edit on Volume of a solid of rotation using “rectangles perpendicular to the axis of revolution”
Oct
14
reviewed Looks OK regression vs classification
Oct
14
answered Why perfect square has odd number of factors
Oct
14
answered Why is ${\sum_{i=1}^n a_i^{n+1}}\bigm/{\sum_{i=1}^{n}a_i^n} \geq \frac 1n{\sum_{i=1}^n a_i}$
Oct
14
answered QR decomposition - does Q always have full column rank?
Oct
13
revised Extend a homeomorphism of an arc of a circle to the entire circle.
added 220 characters in body
Oct
13
comment Show that $f = 0$ almost everywhere in $E$
Couldn't you simply say that $\mu(\{f>\frac1n\})=0$ and $\mu(\{-f>\frac1n\})=0$ and therefore $\mu(\{f\ne0\})=\mu(\bigcup_n \{f>\frac1n\}\cup\{-f>\frac1n\})=0$?
Oct
13
answered Extend a homeomorphism of an arc of a circle to the entire circle.
Oct
13
answered Stuck on a dot product proof
Oct
13
comment Is there a linear transformation who domain isn't all of $\mathbb{R}^n$?
No. Linear (in fact all functions) functions are defined on all of their domain. If one writes $f\colon A\to B$ then $A$ is always the domain. Thus the square root function better be written as $\mathbb R_{\ge 0}\to\mathbb R$.
Oct
13
comment Induction on natural numbers
The whole proof might be simplified by showing and using $$\forall a,b,c\in\mathbb N\colon a\ge b\to ac\ge bc$$ and $$\forall a,b\in\mathbb N\colon a+b\ge a.$$
Oct
13
answered Equivalence Relations assistance needed
Oct
13
comment Is it true that $\left[\sqrt{n}+\sqrt{n+1}+\sqrt{n+2} \right ]=\left[\sqrt{9n+7}\right]$?
See also math.stackexchange.com/questions/477429/… that there is no equation $(5)$ possible
Oct
13
answered Is it true that $\left[\sqrt{n}+\sqrt{n+1}+\sqrt{n+2} \right ]=\left[\sqrt{9n+7}\right]$?
Oct
13
answered Does order matter for the convergence of infinite products
Oct
13
answered Difference between cos 2θ and cos θ/2
Oct
13
answered Prove that this is an equivalence relation and give all the different equivalence classes