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Dec
9
awarded  Caucus
Jul
2
awarded  Curious
Mar
12
awarded  Popular Question
Aug
21
awarded  Yearling
Mar
12
awarded  Popular Question
Feb
28
comment Let $f(x,y)$ be a function of two variables such that $\displaystyle\lim_{(x,y)\to(0,0)}=5$. Which is true?
(b) [...] $f(x,y)$ approaches 5 but NOT REACHING (<- false) 5.
Nov
9
comment linear operator on a vector space V such that $T^2 -T +I=0$
Is it true for a vector space with not a finit dimension ?
Nov
9
answered Counting number of vertices given a graph
Nov
6
comment What kind of quadrilateral is determined by four sides and a diagonal?
@DavidZaslavsky I added a very quick proof for a convex polygon, and your question prove that it's not true for not convex simple polygons.
Nov
6
revised What kind of quadrilateral is determined by four sides and a diagonal?
added 182 characters in body
Nov
6
answered What kind of quadrilateral is determined by four sides and a diagonal?
Jun
27
awarded  Yearling
May
14
comment Dealing with connectness and compactness of matrices.
@srijan ... I have some books at home but no links. For a start wikipedia should be fine (look at the references) and the example from Michael Hardy should help a lot.
May
14
comment Dealing with connectness and compactness of matrices.
@srijan With the right norm you can easily prove the compactness, and with the right continuous function the connectedness. "The only continuous functions from X to {0,1} are constant" this property is commonly use to prove connectedness
May
14
comment Dealing with connectness and compactness of matrices.
@srijan You should try to familiarize yourself with different common norms on matrices, and functions (like the determinant). Then you will have most of the tools to solve this kind of problems.
May
14
comment Dealing with connectness and compactness of matrices.
you should have a look at your math classes, and if you don't have one articles on wikipedia to find all the way you can solve such a problem. For compactness, if I remember what I've learn 8 years ago, in a finite space ou can easily use the sequential definition to prove that it's closed and bounded. (for example with n=1, the set of all symmetric positive matrices is similar to R+ => not bounded and therefore not compact)
Dec
29
answered Showing that $ \prod\limits_{i=0}^{n} {n \choose i}\leq(\frac{2^n-2}{n-1})^{n-1} $
Oct
28
comment Truth and undecidability
@AsafKaragila, that's a surprising coincidence, I was discussing with a friend about this question (truth and indecidability) just half an hour ago, and your comment is pretty much the answer we were looking for ! Thx a lot Asaf.
Oct
28
revised Truth and undecidability
deleted 5 characters in body
Oct
11
accepted Truth and undecidability