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Oct
23
answered Intuition behind product rule of probability
Oct
22
answered Proof of Aristarchus' Inequality
Oct
22
reviewed Approve suggested edit on Polynomial inequality proof
Oct
22
comment Mean value of the image of an exponentiallly distributed time under a smooth curve
$f(t)$ should be $\phi(t)$ in 3.
Oct
22
reviewed Reviewed prove that quadrangle is isosceles trapezoid
Oct
21
comment How prove this $\int_{-\pi}^{+\pi}\cos{(2x)}\cos{(3x)}\cos{(4x)}\cdots\cos{(2005x)}dx>0$
I dont have a solution, just some computation with maple/ WA
Oct
21
comment How prove this $\int_{-\pi}^{+\pi}\cos{(2x)}\cos{(3x)}\cos{(4x)}\cdots\cos{(2005x)}dx>0$
The integral of $\prod_{k=2}^{n}cos(kx)$ seems to be $0$ for values of $n$ congruent to $-1, 0 \mod 4$ and a positive rational fraction of $\pi$ for $1,2\mod 4$
Oct
21
reviewed Approve suggested edit on $x^{y^z}$: is it $x^{(y^z)}$ or $(x^y)^z$?
Oct
20
comment Power series $ \sum_{r=1}^{n}x^{r}=\:?$
Almost surely this has been answered here before
Oct
20
comment $\int_{-\infty}^{\infty} \frac{1}{2\pi} \exp\{ -\frac{1}{2} ((y-x)^2 + x^2) \} dx$
square completion
Oct
20
answered Are there any open mathematical puzzles?
Oct
19
answered Determine $a<0$ such that $\int_a^0 f(x) dx = f(a)$
Oct
18
comment use combinatorial reasoning to calculate $ \sum{\binom{100}{a}\binom{200}{b}\binom{300}{c}}$
To add some reference, this is sometimes known as Vandermonde's convolution
Oct
17
comment How find the minimum of the value of $n$ such $n^2\equiv 1\pmod{1007}$
Am i missing someting? $1$ will do
Oct
16
comment Why do we call it a $\sigma$-algebra?
@Did doesn't make more sense does it? unles they were auto referencing to the Bourbaki trive they are$ even then
Oct
16
comment Why do we call it a $\sigma$-algebra?
In French, we even use the word "Tribu", which makes even less sense
Oct
16
reviewed Looks OK Residue at $0$ of $\frac{1-\cos z}{z^4}$
Oct
16
reviewed Approve suggested edit on Fuchsian Groups: A counterexample
Oct
16
comment Is there a fast way to compute coefficient of some term of the product of some series'?
@user100508 Yes there is someting to do in that case, perhaps ask a new question for that particular case.
Oct
15
comment Is there a fast way to compute coefficient of some term of the product of some series'?
@user100508 Using $A*B$ to be the cauchy product of two series, you could derive that it is in fact a convolution. In particular, it is associative, so for $A*B*C$, start by computing $D=A*B$ and then $D*C$. I do not know of a more elegant formula other than the one you'd get arranging all the sums this process give you