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Martin Cohen is a retired computer programmer who loves dancing (favorites are West Coast Swing, Waltz, Foxtrot, and Salsa), writing (but not revising) poems, and solving math problems (that's why I'm here). He is currently trying to learn improv at the Westside Comedy Theater (westsidecomedy.com) in Santa Monica, CA.

He can also be reached at mjcohen@acm.org.


6h
comment A closed form of $\sum_{k=0}^\infty\frac{(-1)^{k+1}}{k!}\Gamma^2\left(\frac{k}{2}\right)$
My knowledge (or lack of it) usually limits me to moderately elementary methods. I'm glad that I did not make any mistakes in my manipulations.
6h
comment Finding the area of a triangle from vertices? Linear Algebra
So it's an answer Jim, but not as they know it.
6h
comment Proof of convergence of Kaprekar's Constant
I read recently that it is essentially a set of cases, so it's not too illuminating.
6h
comment Alternative function definitions
What do you mean by the "sum rule"? If you mean sin(x+1) = sin x cos y + cos x sin y, you also need cos.
6h
comment Finding whether a sum of numbers in a set generate another number
Once again we see that math is like magic: once you know the true name of something (in this case, "subset sum problem") you can control it.
6h
comment A closed form of $\sum_{k=0}^\infty\frac{(-1)^{k+1}}{k!}\Gamma^2\left(\frac{k}{2}\right)$
Nice use of the Beta function. I didn't think of that when I did my "answer".
6h
answered A closed form of $\sum_{k=0}^\infty\frac{(-1)^{k+1}}{k!}\Gamma^2\left(\frac{k}{2}\right)$
1d
answered Solve for x: sin2 x − cos2 x = sin x, −π ≤ x ≤π
Jul
23
comment Diophantine solution to a fraction
Your solution is definitely better than mine.
Jul
23
answered Diophantine solution to a fraction
Jul
23
revised Is the sequences$\{S_n\}$ convergent?
Added additional information.
Jul
22
comment Is the sequences$\{S_n\}$ convergent?
He did not sum it. He showed that the result is $\frac12 + O(\frac1{n})$.
Jul
18
answered Is the sequences$\{S_n\}$ convergent?
Jul
10
answered “Simple” beautiful math proof
Jul
8
comment What is the range of $f(x,y)=e^{-(x^2+y^2)}$
If $0 < r \le 1$, $f(0, \sqrt{\ln(1/r)}) = r$.
Jul
7
awarded  Yearling
Jul
7
comment A problem with sign of coefficients of a polynomial expression
No. Perhaps seeing what happens in these simplest cases might suggest what to do for the general case.
Jul
7
comment A problem with sign of coefficients of a polynomial expression
Can this be solved for n=1 or 2?
Jul
2
awarded  Curious
Jul
2
awarded  Inquisitive