2,188 reputation
721
bio website qoqosz.net
location Poland
age 25
visits member for 2 years, 7 months
seen Nov 26 at 21:25

I'm just a physics student.


Jul
14
comment Sum equals integral
@RossMillikan If summation of a series would range also from $-\infty$ to $+\infty$ than ${\rm sinc}$ is a nice example.
Jul
14
asked Sum equals integral
Jul
9
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.
Jul
9
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: $$\int_0^1 \frac{f'(x)}{1 + f^2 (x)} \cdot \frac{dx}{f'(x)} \le \frac{\arctan f(1)}{f'(1)} \le \frac{f(1)}{f'(1)}$$
Jun
29
revised Evaluate $\int_1^\infty \cosh^{-1}(x) \ln(x^2-1) \exp \left(- \frac{x}{T} \right) dx $
Fixed formula look
Jun
29
suggested approved edit on Evaluate $\int_1^\infty \cosh^{-1}(x) \ln(x^2-1) \exp \left(- \frac{x}{T} \right) dx $
Jun
28
answered Solving a complex integral
Jun
26
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: $$\frac{\partial \phi}{\partial x} = \frac{\partial \phi}{\partial r} \frac{\partial r}{\partial x} + \frac{\partial \phi}{\partial \theta} \frac{\partial \theta}{\partial x}$$
Jun
26
answered Visualizing Commutator of Two Vector Fields
Jun
26
answered Solving the integral $\int_{0}^{\infty} \frac{\sin{x}}{x} \ dx = \frac{\pi}{2}$?
Jun
26
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.
Jun
26
answered Two sums for $\pi$
Jun
25
comment A linear differential equation
@rubik ok, here it goes.
Jun
25
answered A linear differential equation
Jun
24
revised Series Expansion
added 143 characters in body
Jun
24
answered Series Expansion
Jun
23
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.
Jun
23
comment A linear differential equation
@ZevChonoles so here goes the tag. I think submitting my own solution would spoil the problem a bit.
Jun
23
revised A linear differential equation
edited tags
Jun
23
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 :|