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3h
answered Number of permutations of an integer
3h
answered Borel measure associated to the Cantor singular function
5h
answered A functional equation that is equal to 7x
7h
revised harmonic functions on the disk which agree on the real are identical?
added 97 characters in body
7h
answered harmonic functions on the disk which agree on the real are identical?
8h
revised Chinese remainder theorem for three equations?
added 650 characters in body
10h
comment What is the intent of this problem, disguised as an eigenvalue - eigenvector problem?
Actually it could be a single second eigenvalue with multiplicity $2$. That would be the case if $a=b=c$. In fact the discriminant of the characteristic polynomial turns out to be $36 (a^2 + b^2 + c^2 - ab - ac - bc)(ab + ac + bc)$. There are three distinct eigenvalues when this is nonzero.
11h
comment For a symmetric matrix $X$, is $A^T X^{-1} A$ symmetric for any $A$?
Of course you do have to assume that $X^{-1}$ exists.
11h
comment Digital Roots of Square Numbers
@mathlove Thanks for catching that.
11h
revised Digital Roots of Square Numbers
edited body
11h
revised Runge Phenomena and Taylor Expansion
added 47 characters in body
11h
answered Runge Phenomena and Taylor Expansion
11h
answered Digital Roots of Square Numbers
13h
comment What is the definition of a Critical Point?
"Might" is too vague to use in definitions.
13h
comment What is the definition of a Critical Point?
@MichaelHoppe No, that's a really bad idea, leading to considerable confusion. There are critical points that are not minima or maxima.
1d
awarded  Enlightened
1d
awarded  Nice Answer
1d
revised Chinese remainder theorem for three equations?
added 447 characters in body
1d
answered The Predual of a von Neumann algebra
1d
comment Analytical result for element-wise vector division?
Vector-matrix multiplication? But elementwise division is of no help for that.