Goodarz Mehr
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 Feb 25 comment coloring a $4\times 4$ square with $4$ colors really nice! thanks a lot. the intresting point is, this question was posed for a mathematical olympiad!!! Feb 23 asked coloring a $4\times 4$ square with $4$ colors Feb 21 comment two shapes in a $2n\times 2n$ grid sheet, can we pick third one? @GerryMyerson: I'm really sorry about that, I forgot to write something there. for each $n\in \mathbb N$, the $L$ shape figure containing $2n-1$ squares works in the sense that if we cut three of them out of the sheet, there is no space for another one to be cut. I forgot the word three. sorry again. Feb 20 comment two shapes in a $2n\times 2n$ grid sheet, can we pick third one? Beautiful and elegant solution for this case. can we generalize it to all large $n$? and another question, with the same conditions as above, suppose we have cut one copy of $L$ out of the sheet, can we always cut a second one? Feb 20 accepted two shapes in a $2n\times 2n$ grid sheet, can we pick third one? Feb 20 comment two shapes in a $2n\times 2n$ grid sheet, can we pick third one? yes, they are counted as copies. Feb 19 asked two shapes in a $2n\times 2n$ grid sheet, can we pick third one? Feb 17 comment A subspace is the direct sum of two others I wrote exactly the question's statement. I don't know what condition was in mind of our teacher. Feb 17 asked A subspace is the direct sum of two others Feb 16 asked Number of subspaces not less than cardinality of the field Feb 13 comment finding the derivative thanks, it was nice. Feb 13 accepted finding the derivative Feb 13 asked finding the derivative Feb 6 accepted Computing determinant of a matrix with non-zero values on three diagonals Feb 6 comment Computing determinant of a matrix with non-zero values on three diagonals my solution was like this: let $a_n$ be the determinant of this matrix. then using that formula, I got $a_n=2a_{n-1}-2a_{n-3}+a_{n-4}$. solving this recurrence relation gave me that formula. :) Feb 6 comment Computing determinant of a matrix with non-zero values on three diagonals so my formula agrees with the real determinant for small vlues of $n$, right? I'm so happy about it!!!! Feb 6 asked Computing determinant of a matrix with non-zero values on three diagonals Feb 4 accepted Showing \$\prod\limits_{i