7,221 reputation
1927
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location Boston, MA
age 64
visits member for 2 years, 9 months
seen 17 hours ago

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17h
comment Proving something is a linear transformation?
I think you mean the domain to be $\mathbb{R}^3$.
17h
answered What is this picture?
2d
answered Why is this combinatoric solution not correct?
2d
revised Intersection of two circles.
deleted 2 characters in body
2d
answered Intersection of two circles.
Dec
13
awarded  Caucus
Dec
12
comment What's the difference between a bijection and an isomorphism?
Yes, that's right. Another example would be the map from $\mathbb{Z}\to\mathbb{Z}:n\mapsto n+1$. This is a bijection, but does not preserve addition.
Dec
12
answered What's the difference between a bijection and an isomorphism?
Dec
12
comment Drawing lines from tangents from two circles on both sides.
You don't need the angle; all you need is the slope of the line. The slope of that line is $\frac{4-2}{5-2} = \frac{2}{3}$, so that will be the slope of both tangent lines (and the slope of the lines connecting the two points of tangency to one of the circles will be $-\frac{3}{2}$).
Dec
12
comment Subfield of a Field
$F$ is not a field: $(1,0)\cdot (0,1) = (0,0)$, so that $F$ is not even an integral domain.
Dec
12
answered Drawing lines from tangents from two circles on both sides.
Dec
12
answered Generating functions and central binomial coefficient
Dec
10
revised Why does the hypotenuse differ by one from the non-prime side?
added 13 characters in body
Dec
10
comment Why does the hypotenuse differ by one from the non-prime side?
Yes, try the Wikipedia article on Pythagorean triples.
Dec
10
answered Why does the hypotenuse differ by one from the non-prime side?
Dec
9
comment algebra and applications (Groups)
None of these is particularly difficult; you must have some thoughts.
Dec
9
answered For what $n$ is $n! = 2^8\cdot3^4\cdot5^2\cdot7$?
Dec
8
comment Integration over a spherical surface
You mean you have a (discontinuous) function $f:S^2\to \mathbb{R}$ such that $f(z)=0$ except for one value of $z$?
Dec
8
revised Average number of trials until drawing $k$ red balls out of a box with $m$ blue and $n$ red balls
added 197 characters in body
Dec
6
revised Special case of prime number theorem for arithmetic progressions 4k+1
added 2 characters in body