Mark Hurd
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 Mar 15 revised “This statement is false.” Slightly expanded Mar 15 answered “This statement is false.” Mar 1 comment Are there arbitrarily large gaps between consecutive primes? I was wanting to confirm a gap recently and still have these in my history: Table of Known Maximal Gaps and First occurrence prime gaps. Feb 9 comment Why was the zeta function introduced? The closest I've found is Wikipedia's general introduction to Euler's work, specifically on Analysis where it lists he created, invented and/or proved much of what we use today. The answer to your actual question is probably in one or more of Euler's works. Feb 2 answered Proof verification for $\mathcal{P}(A) \cap \mathcal{P}(B) = \mathcal{P}(A \cap B)$ Dec 15 comment Let $X \subset \mathbb{R}^n$. Suppose that $0 \in X$ and $\|x-y\| = 1$ for $x,y \in X, x \neq y$. Then the maximum number of elements in $X$ is $n+1$. I don't know the details well enough, but can a direct induction proof work? It definitely describes the rigidity of there being only one extra point each time to me (because the other possible point is going to be more than one unit away from the first extra one). Dec 1 comment Confusion about differentials It's not very relevant here, but remember your second formula should be $\int \mathrm{d}y = \int f'(x) \mathrm{d}x + C$. Dec 1 comment How do I explain 2 to the power of zero equals 1 to a child I think there are better ways for convincing someone that $2^0=1$, but I think your argument works well for $0^0=1$ :-) Nov 3 comment Is an arbitrary number of the form xyzxyz divisible by 7, 11, 13? @hkmather802 I assume you've used $\overline{ab}$ to mean $10a+b$, but in which case all $xyz$ should really be $\overline{xyz}$. Oct 13 comment $3\times3\times3$ hypermatrix multiplication Note that currently you're diagram simply describes 2-d matrix multiplication 3 times "deep". I.e. ignore all but the front face and you see normal 2-d matrix multiplication, and then you can see it again in the middle slice and finally in the back face. You need to specify what you want the result to be or do; i.e how it is to behave, and/or at least mention how much of the final result should vary when varying each of the points in the multiplicands. Oct 4 comment Probability of winning in a die rolling game with six players And, clearly, the way to make the game fair is to roll the die first to choose the first player :-) Sep 29 revised How can I introduce complex numbers to precalculus students? The solution is non-complex, as WA shows; it's how to get there I've forgotten. Sep 10 reviewed Reviewed Modular arithmetic with different moduli? Aug 28 revised Finding triplets $(a,b,c)$ such that $\sqrt{abc}\in\mathbb N$ divides $(a-1)(b-1)(c-1)$ Remove spurious *; normalise the colons just to change at least 6 characters. Aug 28 suggested approved edit on Finding triplets $(a,b,c)$ such that $\sqrt{abc}\in\mathbb N$ divides $(a-1)(b-1)(c-1)$ Aug 11 comment Approximating $\pi$ by an expression of the form $\sqrt{\sqrt{ \cdots \sqrt{ n!! \cdots !}}}$ @wltrup Your tongue in cheek answer uses 4 0s and 3 1s. Jul 28 comment 'Obvious' theorems that are actually false If you consider a finite number of sets $V_n$, and take a limit it does seem plausible, not quite obviously false. Jul 9 revised How to prove that $\frac{(5m)!(5n)!}{(m!)(n!)(3m+n)!(3n+m)!}$ is a natural number? Another idea; typo Jul 9 revised How to prove that $\frac{(5m)!(5n)!}{(m!)(n!)(3m+n)!(3n+m)!}$ is a natural number? Another idea Jun 29 reviewed No Action Needed Why is zero the only infinitesimal real number?