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Jul
25
comment Prove that $A,B$ are similar
I assume you mean that $A,B\in M_6(\mathbb{Q})$ and not merely $A,B\in M_6(\mathbb{R})$?
Jul
12
answered Cardinality of $P_\mathfrak{c}(\mathbb R)$
Jul
3
comment Problem in understanding a proof there are five Platonic solids.
@MertAktaş I have no idea, I don't think this site allows that feature.
Jul
2
awarded  Popular Question
Jun
30
revised Catalan's number with a twist
fixed a typo
Jun
30
comment Catalan's number with a twist
@pkacprzak Yes, you're right. Thanks for pointing it out.
Jun
29
awarded  Nice Answer
Jun
29
comment How to express double orthogonal complement?
@autolatry For finite dimensional vector spaces, the double orthogonal complement is indeed the original. This is no-longer true for infinite dimensional spaces (which is the standard context for Hilbert spaces).
Jun
25
comment Is Wolfram Alpha calculating this incorrectly?
I am not certain that the domain issue that the various answers pointed out is the entire story. Otherwise, "does $2\ln|x|$ equal $\ln(x^2)$?" should return true, which it doesn't.
Jun
25
comment What is the combinatorial proof for the formula of S(n,k) - Stirling numbers of the second kind?
Take a look at these notes, section 7.3. The alternating sum should immediately invite you to think of an inclusion/exclusion argument.
Jun
25
comment What is the combinatorial proof for the formula of S(n,k) - Stirling numbers of the second kind?
Which formula are you referring to? Are you referring to the recursive relation? The sum in terms of binomial coefficients? The generating function?
Jun
22
awarded  Good Answer
Jun
10
comment Is it true or false ? (2-connected graph)
As stated, this proposition is trivial. We can just take $x$ and $y$ to be adjacent in $C$. Then $x-y$ is certainly a path which is vertex disjoint from $V(C)\backslash\{x,y\}$. You probably want some edge disjointness condition too.
Jun
2
accepted Cardinality of a Grothendieck Universe
Jun
2
asked Cardinality of a Grothendieck Universe
May
30
answered Why does ${\lambda _i}(A) \ge {\lambda _i}(B)$?
May
30
comment A statement regarding vector spaces…
I could be mistaken, but I don't think the identity $(U+V)\cap (W+V) = (U \cap W) +V$ holds for general subspaces. I don't have a counter-example right now, but I recall the lattice of subspaces being non-distributive. Can you provide justification for that perhaps?
May
27
answered Finding de Dr. Bronowski's number
May
27
answered $\{-n+\frac{1}{n};n\in\mathbb{N}\}=M$ closed in $\mathbb{R}$
May
27
answered prove $\sum \limits_{k=1}^n A(n,k){x+k-1 \choose n}=x^n$