The mathematician formerly known as DayLateDon

27m
revised Prove (or derive) the de Polignac formula for the prime decomposition of $n!$
Added definition of formula in question
1h
comment Prove (or derive) the de Polignac formula for the prime decomposition of $n!$
Is this the formula you mean?
13h
revised If $\cos x = \frac{3}{7}$, then $\sin\frac{x}{2} = ?$
Better title, TeX improvement
14h
comment Show that the orthocenter must coincide with one of the vertices of triangle ABC.
@HarishChandraRajpoot: I hope you realize that what I'm really suggesting is: Please stop making trivial edits to ancient questions.
14h
comment Show that the orthocenter must coincide with one of the vertices of triangle ABC.
@HarishChandraRajpoot: If you must continue cluttering the Active Questions queue with trivial TeX edits to ancient questions, please note that the proper TeX for "$\triangle$" is $\triangle$, not $\Delta$. (We don't want someone dredging these questions back up again just to even-more-trivially re-edit your edits.)
Jul
3
comment Question about the existence of points and lines.
Why doesn't my drawing of a cat purr when I pet it?
Jul
2
comment Special Products of Transpositions
A year later, I get an answer. Hooray! Now, if I could only remember what exactly I was thinking when I asked ... :)
Jul
2
comment How do I generate a sparse invertible 10000 by 10000 binary matrix with 30 to 50 non-zeros per row?
Column swaps are just row swaps of the transpose.
Jul
2
comment How do I generate a sparse invertible 10000 by 10000 binary matrix with 30 to 50 non-zeros per row?
How about the Upper-Triangular approach, but with random row and column swaps?
Jul
1
awarded Nice Answer
Jul
1
revised The position of a ladder leaning against a wall and touching a box under it
Slightly cleaner and more-general argument
Jun
30
answered The position of a ladder leaning against a wall and touching a box under it
Jun
30
comment Proper definition of concyclic?
Provided that you're clear that the same $Z$ and $a$ apply across all $z_k$, then: yes, this is a proper definition.
Jun
30
revised Integrating $\int{\frac{x^2}{1+x^5}dx}$
Better title
Jun
29
revised Make $20$ using two "$3$"s
Better title, edited for clarity, removed irrelevant tag
Jun
27
comment What is happening in the picture
The points moving along the diameters are the feet of perpendiculars to those diameters from a point moving along the circumference.
Jun
27
comment What is happening in the picture
The origin of this appears to be a blog post about the "Van Schooten Ellipse", which has some discussion and links to other ellipse-drawing mechanisms.
Jun
26
answered If $\arctan(x)+\arctan(y)+\arctan(z)=\pi/2$ how to show that $xy+yz+zx=1$?
Jun
26
revised Help to solve this geometry problem
Added missing "2"s in final result.
Jun
25
comment Conversion between trig functions and hyperbolic trig functions
See the Gudermannian function.
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