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16h
comment Distance between the nail and the center of the disk
I think you mean "in order to find $d$ given $l$ and $r$".
16h
revised Space formed by dot products of three vectors
added 37 characters in body
17h
answered Space formed by dot products of three vectors
1d
comment Does there exist a 4D torus with a spherical cross-section, analogous to a circle for the 3D case?
+1. Regarding your final paragraph, it might help the OP to first visualize the two-dimensional torus as a "circular shell" in 2D, i.e. an annulus, whose boundary circles have been glued together (after lifting them up out of the plane into 3D).
2d
comment What is connexity (in simple language)?
"Connexity" appears to be a shopping/marketing website. Did you mean connectivity, convexity, or something else?
2d
comment How do you keep track of what vectors nabla ($\nabla$) should be working in on?
I've never seen $\overleftarrow{\nabla}$ before so maybe I don't understand what's going on. I'll just leave this here: Wikipedia's list of vector calculus identities. Apparently $$\nabla\times(A\times B) = A(\nabla\cdot B)-B(\nabla\cdot A)+(B\cdot\nabla)A-(A\cdot\nabla)B.$$
2d
comment what is the most attractive font to use in a mathematical document?
The question in the title is completely subjective. The question in the body, if interpreted as "How can one make a Word document with mathematical equations be typographically similar to a document produced with TeX?", is reasonable, and the title should be changed to match it.
2d
comment Arc length and curvature for logistic curves
What have you tried so far?
2d
comment Why these arguments for $\frac 00=0$ are not valid?
The parallel postulate is consistent with, but not implied by, Euclid's other axioms, for example. There is a difference between the idea that taking $0/0=0$ does not lead to a contradiction and the idea that $0/0$ must be equal to $0$.
2d
comment Why these arguments for $\frac 00=0$ are not valid?
Okay, that's better. As for your actual question: The problem is that it could be any one of three different questions, "Is defining $0/0 = 0$ consistent with the laws of arithmetic?", "Is $0/0 = 0$ implied by the laws of arithmetic?", and "Why doesn't everybody define $0/0 = 0$ instead of leaving it undefined?" All three of these questions have different answers, and it's hard to tell which one you intend. It would help to clarify what specific question you're looking for an answer to (and not just, say, posting a rant).
2d
comment Why these arguments for $\frac 00=0$ are not valid?
How do you take $a=1/x$ when $x=0$?
2d
comment Why these arguments for $\frac 00=0$ are not valid?
"$0/x=0$ for all real $x$ ... follows from distributivity of multiplication over addition" Please show your working. Also note that to use distributivity of multiplication over addition to conclude something about division you need to also supply a definition of division first.
Dec
17
comment What distribution would describe this?
@GenericNickname: Yes, but linearity of expectation holds for dependent random variables too. Henry is computing the expectation of the sum of random variables $X_i = \{\text{$1$ if basket $i$ is good, $0$ otherwise}\}$.
Dec
17
comment A question in paper “Fitting helices to data by total least squares” writen by Yves Nievergelt in 1996
It looks like your $S$ is the paper's $-S$. That's fine, because in general singular vectors are only determined up to sign: if $A = U\Sigma V^T$ is a singular value decomposition, so is $(-U)\Sigma(-V)^T$.
Dec
16
comment Nonobvious examples of metric spaces that do not work like $\mathbb{R}^n$
By the way, this is a specific case of neuguy's example of distance on a graph, in this case a star graph with three leaves.
Dec
16
comment Is there an error in my matrix proofs (Also: potato quality jpeg errors present)
I prefer to think of it like, $A^3=AAA$ so $(A^3)^T=(AAA)^T=A^TA^TA^T=AAA=A^3$.
Dec
15
comment Is indefinite integration non-linear?
@Henning, vadim123: Ah, so you actually just define $0[x]$ to be $[0]$. It would be helpful to add those definitions to the answer, because a naive interpretation of the notation (as in my previous comment) can lead to errors.
Dec
15
comment Is indefinite integration non-linear?
I want to like this answer, but I don't see how $0[x]=[0]$. Zero times any function in $[0]$ is identically zero, so the result collapses to the singleton $\{0\}$, not $\{C:C\in\mathbb R\}$.
Dec
15
revised Number of samples needed to get a given expected distance
added 727 characters in body
Dec
15
awarded  Caucus