Grigory M
Reputation
11,535
365/400 score
 2d revised Splitting equilateral triangle into 5 equal parts url fixed 2d revised Splitting equilateral triangle into 5 equal parts edited title Apr 8 comment Proof of the binomial identity $\displaystyle\binom{m}{n}=\sum_{k=0}^{\lfloor n/2 \rfloor} 2^{1-\delta_{k,n-k}} \binom{m/2}{k} \binom{m/2}{n-k}$ Apr 8 comment Proof of the binomial identity $\displaystyle\binom{m}{n}=\sum_{k=0}^{\lfloor n/2 \rfloor} 2^{1-\delta_{k,n-k}} \binom{m/2}{k} \binom{m/2}{n-k}$ that's just a special case of en.wikipedia.org/wiki/Vandermonde%27s_identity Feb 5 awarded Notable Question Jan 15 reviewed Close Solve the equation $2φ(x)=x$ for $x\in\mathbb N^+.$ Jan 14 awarded Nice Question Dec 30 reviewed Close The ring of real convergent sequences is Noetherian Dec 29 reviewed Leave Closed Prove $(1+2+…+k)^2 = 1^3 + … + k^3$ using induction Dec 25 comment Combinatorial explanation for why $n^2 = {n \choose 2} + {n+1 \choose 2}$ coloured squares also can be counted visually: mathoverflow.net/questions/8846/proofs-without-words/8847#8847 Dec 17 reviewed Close Why does $f:[a,b] \rightarrow \mathbb{R}$ need $f$ to be continuous on $[a,b]$ but only differentiable on $(a,b)$, in some theorems. Dec 16 reviewed Leave Open What is the limit of $\frac{1}{\sqrt{n}}\sum_{k=1}^n\frac{1}{\sqrt{2k-1}+\sqrt{2k+1}}$? Dec 16 reviewed Leave Open Vanishing Gaussian curvature Dec 16 reviewed Looks OK Is an undefined equality vacuously true? Dec 16 reviewed Looks OK What is the value of the finite sum? Dec 16 reviewed Looks OK Finding the logarithm of a matrix? Dec 14 comment How does one read $\bar{A}$ aloud in Russian? «A с чертой» is frequently used (have never heard «A с надчеркиванием» in my life) Dec 14 reviewed Leave Closed How does one read $\bar{A}$ aloud in Russian? Dec 14 reviewed Close How do you pronounce (partial) derivatives? Dec 14 reviewed Close Why is $\sinh$ often pronounced “shine”?