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 Jul14 comment Sum equals integral @RossMillikan If summation of a series would range also from $-\infty$ to $+\infty$ than ${\rm sinc}$ is a nice example. Jul14 asked Sum equals integral Jul9 comment Find the functions family that satisfies the inequality $\int_0^1 \frac{dx}{1+f^{2}(x)} <\frac{f(1)}{f'{(1)}}$ @Mercy it is derivative which is not increasing. Jul9 comment Find the functions family that satisfies the inequality $\int_0^1 \frac{dx}{1+f^{2}(x)} <\frac{f(1)}{f'{(1)}}$ Here's my first though: If we assume that: $f'$ is continuous and not increasing; $f'(1) \neq 0$; $f(0) = 0$; $f(1) \ge 0$, than: $$\int_0^1 \frac{f'(x)}{1 + f^2 (x)} \cdot \frac{dx}{f'(x)} \le \frac{\arctan f(1)}{f'(1)} \le \frac{f(1)}{f'(1)}$$ Jun29 revised Evaluate $\int_1^\infty \cosh^{-1}(x) \ln(x^2-1) \exp \left(- \frac{x}{T} \right) dx$ Fixed formula look Jun29 suggested approved edit on Evaluate $\int_1^\infty \cosh^{-1}(x) \ln(x^2-1) \exp \left(- \frac{x}{T} \right) dx$ Jun28 answered Solving a complex integral Jun26 comment gradient in polar coordinate by changing gradient in Cartesian coordinate You wrote: $$\frac{\partial \phi}{\partial x} = \frac{\partial \phi}{\partial r} \frac{\partial r}{\partial x}$$ instead of: $$\frac{\partial \phi}{\partial x} = \frac{\partial \phi}{\partial r} \frac{\partial r}{\partial x} + \frac{\partial \phi}{\partial \theta} \frac{\partial \theta}{\partial x}$$ Jun26 answered Visualizing Commutator of Two Vector Fields Jun26 answered Solving the integral $\int_{0}^{\infty} \frac{\sin{x}}{x} \ dx = \frac{\pi}{2}$? Jun26 comment Two sums for $\pi$ @daniel I missed the link :( Ok, I'll try to make it more complete and then I'll post it there. Jun26 answered Two sums for $\pi$ Jun25 comment A linear differential equation @rubik ok, here it goes. Jun25 answered A linear differential equation Jun24 revised Series Expansion added 143 characters in body Jun24 answered Series Expansion Jun23 comment A linear differential equation @ZevChonoles maybe I should just delete this topic? I didn't know that posting some (imho) interesting problems will be such a trouble. Jun23 comment A linear differential equation @ZevChonoles so here goes the tag. I think submitting my own solution would spoil the problem a bit. Jun23 revised A linear differential equation edited tags Jun23 comment A linear differential equation @ZevChonoles I know this poem, as well as a solution. I though some of math.SE users would find this problem interesting :|