Forum: Lounge
2009-08-31, 07:48
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Replies: 28
Views: 2,075
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Forum: Puzzles
2009-05-07, 15:24
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Replies: 16
Views: 1,230
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Forum: Puzzles
2009-05-05, 16:15
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Replies: 16
Views: 1,230
Lines in a Square
Consider an n x n chessboard.
What is the size of the smallest collection of lines such that every square of the chessboard is intersected by at least one line ?
PS: I do not pretend to have a...
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Forum: Puzzles
2009-04-27, 15:49
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Replies: 33
Views: 2,120
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Forum: Puzzles
2009-04-24, 15:09
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Replies: 33
Views: 2,120
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Forum: Puzzles
2009-01-26, 10:46
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Replies: 22
Views: 1,390
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Forum: Soap Box
2008-12-16, 09:48
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Replies: 820
Views: 43,612
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Forum: Math
2008-11-07, 14:29
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Replies: 3
Views: 553
Obviously, we can write
\prod_{1\le j<i\le...
Obviously, we can write
\prod_{1\le j<i\le n}(i-j)=\prod_{i=1}^n (i-1)!
I used the pigeonhole approach to prove the result for small n. But even for small n, you cannot use this method in a...
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Forum: Math
2008-11-07, 12:11
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Replies: 3
Views: 553
Looking for an elementary demonstration
a_1,\ldots,a_n
are integers, all different. It is possible to prove that
\prod_{i< j}(i-j) |\prod_{i<j}(a_i - a_j).
Either by using some techniques with Vandermonde Determinants or by proving a...
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Forum: Lounge
2008-05-27, 12:26
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Replies: 5
Views: 652
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Forum: PrimeNet
2008-05-07, 12:22
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Replies: 311
Views: 22,287
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Forum: Lounge
2008-03-27, 09:15
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Replies: 75
Views: 3,480
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Forum: Puzzles
2008-03-20, 11:32
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Replies: 20
Views: 1,010
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Forum: Math
2008-03-06, 09:58
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Replies: 15
Views: 1,693
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Forum: Math
2008-03-06, 09:14
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Replies: 15
Views: 1,693
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Forum: Puzzles
2008-02-13, 15:47
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Replies: 23
Views: 1,140
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Forum: Puzzles
2008-01-29, 09:29
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Replies: 54
Views: 2,935
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Forum: Chess
2008-01-18, 12:16
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Replies: 42
Views: 6,104
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Forum: Lounge
2007-11-26, 10:43
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Replies: 289
Views: 15,077
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Forum: Puzzles
2007-11-14, 07:23
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Replies: 14
Views: 1,193
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Forum: Puzzles
2007-11-13, 16:01
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Replies: 14
Views: 1,193
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Forum: Puzzles
2007-11-13, 15:22
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Replies: 14
Views: 1,193
Composite checkerboard
The numbers 1,2,...,100 are written in cells of a table 10 x 10, each number is written once. By one move, we may interchange numbers in any two cells.
After how many moves may we get a table, in...
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Forum: Homework Help
2007-11-12, 14:12
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Replies: 10
Views: 1,027
actually, I am not sure whether it would fall...
actually, I am not sure whether it would fall under rule 3 "overt answer".
Would "overt" mean that when the response given is handed in as homework answer, the homeworkee receives at least 80 % of...
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Forum: Homework Help
2007-11-12, 14:07
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Replies: 10
Views: 1,027
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Forum: Homework Help
2007-11-12, 13:35
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Replies: 10
Views: 1,027
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