Alex Nelson
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 Jun 17 comment How to compute this integral involving sech? What have you tried? (And is $\epsilon$ "small and positive"?) Jun 17 revised How to compute this integral involving sech? Updated TeX formatting slightly Jun 17 suggested approved edit on How to compute this integral involving sech? Jun 17 comment Question on $\mathfrak{sl}(2,\mathbb R)$ @PeterFranek, could you remind me why it's not a group? I thought it was a subgroup (since it has the identity element and the Baker-Campbell-Hausdorff formula suggests it is closed under multiplication, right?) but rarely is it the full group...am I mistaken? Jun 8 comment Intuition behind the definition of a derivative by Lang Maybe it's because I'm drunk, but isn't the $\lambda y$ term merely the linear term (i.e., derivative) and $\varphi(y)$ the "bonus parts which vanish in the appropriate limit"? Just as if for a usual function in calculus 101 we would Taylor expand $f(x+h)=f(x)+f'(x)h+g(h)$ where $g(h)\sim o(h^{2})$. The derivative would naturally be the linear (first) term...well, the coefficient to $h$... May 18 awarded Yearling May 11 comment What's the term for a “physical vector space”? @RobertIsrael perhaps use the "accountant's trick" and let negative fruit be a deficit owed to someone, and fractional fruit be a fraction of a fruit? (It works in Sraffian economics!) May 9 answered Identifying a power series May 3 comment How would you evaluate $I:=\int_ {0}^{\infty} \frac {\cos(ax)} {(x^2 + b^2)^n} \ \mathrm{d}x$? Consider the real part of the integral $\int(x^2+b^2)^{-n}\exp(iax)\,\mathrm{d}x$ might help... Apr 22 comment What's the name of this category Isn't it isomorphic to the category $C_{A\times B}$? Apr 20 awarded Organizer Apr 20 revised Why the $\zeta$ letter is like this? Fixed tags Apr 20 suggested approved edit on Why the $\zeta$ letter is like this? Apr 20 comment Link between a topological space and a manifold The topology is the collection of open sets of the space (by definition, a member of the topology is called an "open set"). But when a manifold "locally looks Euclidean", you're talking about charts...the image of a chart is itself an open set in the manifold, which requires a topology to talk about... Apr 20 comment Why the $\zeta$ letter is like this? @Goos, the difference is really negligible. Once you get one method of writing a zeta, it's not terribly difficult to deform the orthography into the one you desire. But starting with some zeta, I found, has been the hard part (for me anyways). Apr 20 comment Why the $\zeta$ letter is like this? foundalis.com/lan/hw/grkhandw.htm Apr 18 awarded Civic Duty Apr 15 comment Solve $\sqrt{1+\sqrt{1-4x^2}}=x\left( 1+\sqrt{1+\sqrt{1+2\sqrt{1-4x^2}}}\right).$ Perhaps set $u=\sqrt{1-4x^{2}}$, so $x = \sqrt{1-u^{2}}/2$ and the problem becomes $2=\sqrt{1-u}(1+\sqrt{1+\sqrt{1+2u}})$...? Apr 11 revised Evaluate $\int_{0}^{\pi/4}\frac{6 - 6\sin^{2}(x)}{2\cos^2(x)} \mathrm{d}x$ Improved the tex formatting Apr 11 suggested approved edit on Evaluate $\int_{0}^{\pi/4}\frac{6 - 6\sin^{2}(x)}{2\cos^2(x)} \mathrm{d}x$