miracle173
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 55m comment Find all functions $f(f(f(…(f(x_1,x_2),x_3),…),x_{2016}))=x_1+x_2+…+x_{2016}$ Your picture of the text contains 17 lines, 14 are unrelated to the problem. You should change this. Also you didn't add a reference for your problem, e.g., which contest. You "work so far" shows not much effort. It maybe important that n=2007 and not n=2016. But you can start with n=3. This makes the structure of the problem simpler. Maybe this brings some insight after some work. 5h comment Supposed p is a prime Number such that (p-1)/4 and (p+1)/2 are also primes. Show that p=13 Please make your post more readable and ude $LaTeX$ 23h comment The probability distribution @AndyK I don't think that this is a $LaTeX$ specific term. It is about programs in general and describes a chunk of code that "will allow readers to copy-and-paste-and-compile your code and see exactly what problems you might be experiencing". I can't see how this is useful in this context. 1d comment The probability distribution Please show us your efforts. 1d comment I want to show that $x^2 - x + C\epsilon\ge 0$ under some assumption. if $x=5$ what is your sufficiently small $\varepsilon$? 1d comment I want to show that $x^2 - x + C\epsilon\ge 0$ under some assumption. That sentence make no sense. If yo want to assume that $x \le 1/2 \sqrt\epsilon$ then assume it. But again, your formulation does not make no sense. 1d comment I want to show that $x^2 - x + C\epsilon\ge 0$ under some assumption. "Let $x\ge 0$. For sufficiently small $\epsilon>0$, assume that $x\le \sqrt\epsilon$." That does not make sense. Given $x$ you have to make $\epsilon$ sufficiently large, to make $\sqrt\epsilon$ greater than $x$, not to make it sufficiently small. Or maybe you want to say only "Assume that $x\le \sqrt\epsilon$" Apr 29 comment Why is The Following equality true? (limit of a sum and integrals) en.wikipedia.org/wiki/Riemann_sum#/media/… Apr 29 comment What is the value of $k^2$ is $f`$ a typo or should it be $f'$ (with a single apostrophe) Apr 28 comment Right Triangle's Proof You write "Wikipedia" but you link to mathworld.wolfram.com/PythagoreanTriple.html . All in all it is a rather complicated and inelegant way to prove this simple fact. Apr 28 comment A simple cubic equation problem: And why can I suppose that $z_3=\dfrac{1}{\bar{z_1}}$? Apr 28 comment Right Triangle's Proof But if you check this three cases you get $b^2$ is $63$, $44$ or $23$. So 12 actually can't be the lenght of the hypotenuse because none of these numbers is a perfect square. Apr 28 comment Right Triangle's Proof No, I said if you want to check if 12 is the length of the hypotenuse $c$ you only have to check the three cases where $a$ is $9$, $10$ or $11$. Apr 28 comment A simple cubic equation problem: How does this imply that tthere is a root with absolute value 1? Apr 28 comment Solution of functional equation $f(x+y)=f(x)+f(y)+y\sqrt{f(x)}$ So there are four solutions. Apr 28 comment Solution of functional equation $f(x+y)=f(x)+f(y)+y\sqrt{f(x)}$ $f(x) =0$ is a solution, too.And $f(x)=0$ if $x<0$ and $f(x)=\frac{x}{4}$ if $x \ge 0$ ... Apr 25 comment Why can't a open interval in $\mathbb{R}$ be compact? how are compactness and sequentially compactness related? Apr 16 comment Logic Behind Epsilon-Delta Proofs (Single-Variable Calculus) I only read your first formula. you should use a consistent notation, e.g. $\lim_{x \to a} f(x) = L \Leftrightarrow \forall \epsilon >0\;(\exists \delta>0\;(\forall x \in D\;(0 < |x-a| < \delta \implies |f(x)-L| < \epsilon)))$\$ Mar 31 comment Prove a group G is abelian if it satisfies x^2 = x for every x in G It is correct. But too much proof for G={e}. Nevertheless I don't understand the downvotes. Mar 23 comment Can anybody give me a pictorial representation Do you want to say that an open interval is a countable union of disjoint closed intervals?