ybungalobill
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 Aug 22 comment Is there a lower bound for $\int_{B_{r}}f$ when $f$ is a positive function? Having $c$ depend of $f$ makes no sense, as then you can take $c = \frac{\int f}{\omega_n r^n}$ to get a tight bound. Dec 27 comment Radius of convergence of $\sum \frac {a_n}{b_n} z^n$ @martycohen: take $x_n = \sqrt[n]{\frac{|a_n|}{|b_n|}}$ and $y_n = \sqrt[n]{|b_n|}$, then apply the inequality I said and divide both sides by $\limsup y_n$. Dec 26 comment Is this proof, that $\sqrt{n}$ is irrational for all non-square $n \in \mathbb{N}$, correct or not? It should be $nq^2 = p^2$. Dec 25 comment How can I find maximum and and minimum values of $f(x,y)=xye^{-(x+y)}$? @MuhammadKhalifaTranCer: see the calculations posted. Dec 25 comment How can I find maximum and and minimum values of $f(x,y)=xye^{-(x+y)}$? @MuhammadKhalifaTranCer: I do not know your calculations. Likely you forgot one of the cases somewhere. I can try to post the calculations here, but they are likely to be different from yours, so I can't say whether it is beneficial for you. Dec 25 comment How can I find maximum and and minimum values of $f(x,y)=xye^{-(x+y)}$? @MuhammadKhalifaTranCer: Nope. You have $y=0$ or $x=1$. The same goes for $f_y$. But this only gives you the interior points, which according to wolfram happen to not be the maxima and minima in the region. The extrema actually achieved on the boundary, which is the second half of the question. Dec 25 comment How can I find maximum and and minimum values of $f(x,y)=xye^{-(x+y)}$? @MuhammadKhalifaTranCer I don't think so. Recheck your computations. Dec 25 comment How to find the limits by using series Please write the formula using LaTeX, otherwise it is unclear what you mean. Dec 25 comment (Ir)reducible polynomial over $\mathbb{Z}$ What do you mean "irregularly polynomial"? Perhaps you meant "irreducible polynomial"? Dec 22 comment Zeros of Fourier transform of a function in $C[-1,1]$ +1 for solving this in an interesting way :). See the "intended" solution posted by me. Dec 20 comment Zeros of Fourier transform of a function in $C[-1,1]$ OK. Actually what I said (except that for ratio I meant product) is equivalent to the question of whether $\Im h(z)$ may grow faster than $\Re h(z)$. I'll see if I can apply Cauchy-Riemann equations. Does it even sound correct? Dec 20 comment Zeros of Fourier transform of a function in $C[-1,1]$ Everything is fine except for the missing part ... Except for the intuition that near essential singularities the function goes crazy enough, I cannot see why $\frac{h(z)}{z}$ cannot maintain an almost imaginary ratio with $\frac{z}{|z|}$ so that its image would still be almost all of $\mathbb{C}$ yet the real part of the product would remain close to zero. Dec 12 comment problems about normal subgroups and the index Please check the wording of the first item. You first define $K$ and then talk about $N$, and I think it should be $([G:N],|H|) = 1$. Dec 9 comment Uniform convergence of difference quotients to the derivative I'm looking at it for 10 minutes and cannot get why $U_\delta$ is open. It would be so for any fixed $h$, but how it follows when $U_\delta$ is effectively an infinite intersection of open sets (one for each $h$)?