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 Mar 25 comment Euler characteristic equation for circle i wonder if approximating the circle with a regular $n$-gon will work... Mar 25 comment Counting nonidentity elements in a group @snulty thanks, corected Mar 23 comment Proving Discreteness of the Harmonic numbers @almagest we were using a different definition. I was taught that discrete means countable. You are using a different definition... Mar 22 comment Can Levenberg-Marquardt be used to find a local minimum of a function? MATLAB certainly uses Levenberg-Marquardt for straight minimization Mar 22 comment Sum of $\sum \limits_{n=0}^{\infty} \frac{1}{(kn)!}$ sum diverges at $k=0$ and conveges to $\cos (ix)$ for $k=2$ Mar 22 comment a minoration of $P(X>x)$ with $X~N(0,1)$ could you please update the question with your own thoughts on the problem and we will be happy to guide you further. Mar 20 comment Any simpler expression for$\frac{\sum_{k=2}^{n-2}{k\big(\sum_{i=0}^{n-2}\frac{(-1)^i}{i!}\big)}}{n\sum_{i=0}^{n}\frac{(-1)^i}{i!}}$ note your numerator is just a product of 2 sums, the first is arithmetic series $\sum_k k$ and the second is close to $1/e$, so the second factor will roughly cancel the sum in the denominator... Mar 18 comment Show that $\exp(-\lambda x) \cdot\exp(\lambda x)=1$ using the power series see another update2... Mar 18 comment Covering space of a graph is again a graph - why?? unfortunately not... haven't seen this in 3 years... Mar 18 comment Covering space of a graph is again a graph - why?? @Zero unfortunately not Mar 16 comment Central limit theorem for distribution peak rather than mean yes, thank you very much Mar 16 comment How to find this area by integration? are you looking for area and not volume? so surface area then? Mar 16 comment Central limit theorem for distribution peak rather than mean i couldn't get what you are asking -- the CLT does not depend on the underlying distribution of the $X_i$, it can be asymmetric or even discrete. Mar 15 comment endpoints convergence after integrating/mutiplying /subtracting power series i think for 1,2, the endpoints don't have to be checked; since it diverges for the first series, the result will diverge also unless it's a special power series, e.g. the zero function :). (4) is correct, (3) I am not sure. Mar 15 comment Why are complex numbers allowed to be combine like this? i altered your fractions on the left to give you an example of how to format, but your RHS is incomprehensible, can you alter it into readable form that is mathematiccally equivalent of the LHS to make your point? Mar 14 comment Martingale property for two stochastic processes $e^{B_t}$ has lognormal distribution Mar 14 comment Inequality involving triangle yes, you can have an equilateral triangle -- then all inequalities hold as equalities, so $4\sqrt{3}$ is sharp Mar 14 comment Martingale property for two stochastic processes $B_t-B_s|\mathcal{F}_s$ has normal distribution with mean $0$ and variance $t-s$ Mar 13 comment Constructing a partition and sigma algebras what is $\sigma(E)$? Mar 11 comment Integrate $\int \frac{ e^{\tan^{-1}x}}{(1+x^2)^2} dx$ you want to use a substitution $u = \tan^{-1} x$ so $du = \frac{dx}{1+x^2}$, not sure how to get rid of the second $(1+x^2)$ in the denominator