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18h
answered Please help me with this sigma notation
1d
comment Four definitions for Borel algebra in $\mathbb{R}$?
Plus, in this group, show your own work and where you got stuck.
1d
comment Is $\sqrt{x}$ Lipschitz continuous on $(0,\infty)$?
According to MVT, for a differentiable function, "Lipschitz" means "bounded derivative". The interest in Lipschitz is: certain properties of differentiable functions can be proved even for non-differentiable (but Lipschitz) functions.
2d
comment a mod -b (Maple disagrees with Wolfram)
Maple. For "77 mod (-25)" it returns "2" ... I don't know why you thought Maple did not do this. Of course the character "%" has a completely different meaning in Maple.
2d
comment Calculating the residue of a complex funciton with ln(z) at z=0
What is your definition of "resudue"? The one I know requires a function analytic in a punctured neighborhood of the point. This one is not.
Aug
31
answered differential equations solvable only by numerical methods
Aug
30
answered Why do we write $df/dx$ instead of $df/dx(x)$?
Aug
30
comment Evaluation of $ \int_{-\infty}^{\infty}\arctan (\frac 1{2x^2})\ \mathrm dx$
I think it is unreasonable to expect a connection. Integral $\int_1^\infty (1/x^3)\,dx=1/2$ but I doubt that helps in evaluating $\sum_{n=1}^\infty 1/n^3 = \zeta(3)$.
Aug
30
comment Evaluation of $ \int_{-\infty}^{\infty}\arctan (\frac 1{2x^2})\ \mathrm dx$
Why do you think the integral is related to the sums?
Aug
30
comment Branch cut of $\sqrt{z}$
Your notation here is a bit off. Try to come up with a situation where your proposal would be useful.
Aug
30
comment What makes it legitimate to multiply both sides?
Your "operation" is a "function". And functions have this property (the "vertical line property"): if $x_1=x_2$, then $f(x_1)=f(x_2)$.
Aug
28
comment Find all functions f such that $f(f(x))=f(x)+x$
OK, how to prove surjective in the decreasing case?
Aug
28
revised Find all functions f such that $f(f(x))=f(x)+x$
added 25 characters in body
Aug
28
revised Find all functions f such that $f(f(x))=f(x)+x$
added 206 characters in body
Aug
28
answered Find all functions f such that $f(f(x))=f(x)+x$
Aug
28
awarded  Nice Answer
Aug
27
answered Is there anything wrong with this proposed proof of the irrationality of Euler's constant?
Aug
27
comment Does “$\dots$” imply countability?
You can probably find things like: consider the set of real numbers $0, \cdots, 1$.
Aug
27
answered Solving the integral $\int_{-\infty}^{\infty} (1+x^2)^{-3/2}$ with $\sinh$, $\cosh$?
Aug
27
comment I am trying to find where $\sin ( \pi t) e ^{ -t } $ converges via secant method and I keep getting this error below with my code.
You mean this is not the place to come for free code debugging?