92,130 reputation
581169
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 48
visits member for 1 year, 7 months
seen 9 hours ago

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


Jul
8
comment game theory - coin flipping game
If $A$ ends with more than her initial bankroll, $B$ should read th ebook How to gamble if you must and use bold play. By reading the same book, $A$ can calculate $B$'s winning probability given her current amount and will base her betting decision on that (though it's still not easy for $A$)
Jul
8
comment game theory - coin flipping game
What happens when both have the same amount of play-money when the game ends?
Jul
8
answered Roulette betting system probability
Jul
8
comment Show that if $b\mid c$ and $b > \gcd(c, d)$, then $b\nmid d$.
It's enough to say that $b$ is a commn divisor, hence cannot exceed the greatest common divisor (if the latter is defined with its literal meaning).
Jul
8
answered Prove that f(x)=g(x)
Jul
8
comment How can I construct a square using a compass and straight edge in only 8 moves?
It appears that extending a line does not count against yuor score!?
Jul
8
comment Number of integer distance grid points in a cubic grid
Hm, let's argue for a physicist with physical approximations ;) The value of $x^2+y^2+z^2+\ldots$ (if it is approximately $R^2$) is a perfect square with probability $\approx\frac1{2R}$, so the growth yould be expected to be $\sim k^{n-1}$ instead of the $k^n$ from user1086219's answer ...
Jul
8
comment Prove that $\frac{100!}{50!\cdot2^{50}} \in \Bbb{Z}$
@Mark If you jointly permute the $1$s, $2$s, and so on ...
Jul
8
reviewed Approve suggested edit on Banach algebra with unit
Jul
8
comment Volume of irregular solid
I don't understand how your solid is described. Is your solid a polyhedron, i.e. bounded ba finitely many palnar faces between finitely many vertices?
Jul
8
answered If $f_n\to f$ uniformly on [a,b] and f is continious on [a,b] then $f_n$ is continious in [a,b]
Jul
7
reviewed Approve suggested edit on For All Unique Combinations of 60 A's and 20 B's Number of Combinations that have BB
Jul
7
comment Find all real numbers such that $\sqrt {x-1/x } + \sqrt {1 - 1/x} = x$
foiled again :)
Jul
7
answered Find all real numbers such that $\sqrt {x-1/x } + \sqrt {1 - 1/x} = x$
Jul
7
revised Find all real numbers such that $\sqrt {x-1/x } + \sqrt {1 - 1/x} = x$
added 6 characters in body
Jul
7
comment Total perimeter of rectangeles covering the boundary of a Jordan-measurable set in in $\mathbb{R}^2$
If you take the unit disk, you can achieve a perimeter of $\approx 16$. With wilder shapes such as $\{\frac1n|n\in\mathbb N\}\times [0,1]$, the perimeter will grow to infinity as you try to decrease the area.
Jul
7
comment Show $\sum_{i<j} |a_i a_j| b_{ij} \leq \sum_{i=1}^{n} a_i^2 \max_{1 \leq i \leq n} \sum_{j=1}^{n}b_{ij}$
It still doesn't hold, now it claims (with $b_{ij}=-1$, $a_i=1$) that $-{n\choose 2}\le -n^2$. I'd suspect that non-negative values are postulated, but the absolute value bars make that less likely.
Jul
7
reviewed Leave Open When zero-divisor graph is planar?
Jul
7
comment Show $\sum_{i<j} |a_i a_j| b_{ij} \leq \sum_{i=1}^{n} a_i^2 \max_{1 \leq i \leq n} \sum_{j=1}^{n}b_{ij}$
This does not hold. If all $b_{ij}=-1$ and all $a_i=1$, then this claims $-{n\choose 2}\le -2n^2$
Jul
7
comment How to prove $4^n+1$ is prime number if $3^{\frac{q-1}{2}} \equiv-1 \mod q$?
$(\mathbb Z/q\mathbb Z)^\times$ is always a multiplicative group, it is the group of units of the ring $\mathbb Z/q\mathbb Z$ and has $\phi(q)$ elements.