92,325 reputation
581169
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 48
visits member for 1 year, 7 months
seen 30 mins ago

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


19m
comment Example of dependent but conditional independent
$P(Y)=P(Z)=\frac12$, but $P(Y,Z)=\frac12\cdot \frac34\cdot\frac34+\frac12\cdot\frac14\cdot\frac14=\frac5{16}\ne\frac14$.
26m
comment Lower bound of the index of a subgroup of a non abelian simple group
You mean proper subgroup.
52m
comment Need to negate this proposition!
The "and" between quantors better viewed as a "such that".
1h
comment A and B are sets. Prove that A=B iff P(A) = P(B) where P is the power set.
Just note that $\bigcup P(A)=A$.
1h
comment How to get a number that is divisible by $n$ - without obviously seeing it?
@user2345215 D'oh, if you want to read a recipe that enforces divisibility, your mind simply ignores such crucial words. :) - Jsut like sentnces with lots of msipselld words are stlil more or less raedable ...
1h
comment sub-algebra of continuous real valued functions without unit must vanish at a point
Don't we need proper subalgebra?
2h
comment How to get a number that is divisible by $n$ - without obviously seeing it?
Well, let's see. Think of a three-digit number, but not ending in zero or five and digit sum not a multiple of three. Now take it to the eighth power and subtract one. I magically foresee that the result is divisible by fifteen. - Your audience won't like you.
5h
comment Solve an Angle-Side-Angle special case triangle if it has an obtuse angle?
Why dont you try the law of sines? It works.
5h
comment Compact sets of real number
Can you use that a continuous function on a compact set attains its minimum? Or that the product of compact spaces is compact?
5h
comment Insights in solving systems of eqn?
The for the moment forget about $I_3AI_4$, whatever that is. Try to obtain new - simpler - equations by adding / subtracting known equations. For example, add the first and third to immediately see what $x_3$ must be ...
8h
comment In how many ways can i build this String : abbcccdddd?
As it seems, there is only one way :)
9h
comment Dual Vector Space embedding
In the first line you ask for an embedding, in the last line for a natural embedding. These are different questions (and have different answers).
9h
comment Logarithm of a negative number
Nothing. You dropped the condition "whenever $a,b>0$" from the full steatement of the identity.
9h
comment When do eigenvectors converge?
If $\{v_n\}_{n\in\mathbb N}$ is a sequence such that $A_nv_n=\lambda v_n$, it is not necessarily the case that $v_n$ converges in the first place. Think of $A=A_n=I$, $\lambda=\lambda_n=1$ for all $n$ and $v_n$ some "random" sequence.
9h
comment Please give feedback to this solution.
The "closed as duplicate" is possibly not fully justified. The duplicate asks whether we can conclude that $n$ is prime if it has no divisor $<10^6$ (and we have $n\gg 10^{12}$); the answer is of course "no". This question aks the same if it is known that $n$ has no prime divisor $<n-10^6$; here the answer is "yes" as soon as $n>1001001$, say). - The fact that the actual $n\gg10^6$ chosen can be explicitly factored doesn't touch the question as such.
14h
comment Every integer greater than 1 is divisible by at least one prime. Can anyone please express this in logical notation
Do you have predicates for "is integer", "is greater than", "divides", "is prime" and a constant symbol for "1" available?
14h
comment Exercises in combinatorics
Where do cycles come from in 3)?
14h
comment Irrationality of $\pi$ and circumference to diameter ratio.
Note that $\frac13$ also has "never ending numbers after decimal". This doesn't contradict the fact that $\frac13$ is finite.
1d
comment exercise involving exactness
I assume here monomorphism only means left-cancelable?
1d
comment prove that commuting ring is a subring of E(M) .
$E(M)$ is a ring with pointwise addition as addition and composition as multiplication. But that is in general not commutative.