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4h
comment Is this matrix invertible?
However, it does appear that the determinant factors as the product of a power of $x$ and cyclotomic polynomials in $x$.
6h
comment Under the Borel measure associated to the Cantor function each of the intervals remaining in the construction of the Cantor set has measure $2 ^{-n}$
By construction of the Cantor function: as you said, at the $n$'th step you remove an interval of length $2^{-n}$ from the middle of each interval of length $2^{1-n}$, leaving intervals of length $2^{-n}$.
10h
awarded  Nice Answer
15h
revised Number of permutations of an integer
deleted 397 characters in body
19h
answered Number of permutations of an integer
20h
answered Under the Borel measure associated to the Cantor function each of the intervals remaining in the construction of the Cantor set has measure $2 ^{-n}$
21h
answered A functional equation that is equal to 7x
1d
revised harmonic functions on the disk which agree on the real are identical?
added 97 characters in body
1d
answered harmonic functions on the disk which agree on the real are identical?
1d
revised Chinese remainder theorem for three equations?
added 650 characters in body
1d
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.
1d
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.
1d
comment Digital Roots of Square Numbers
@mathlove Thanks for catching that.
1d
revised Digital Roots of Square Numbers
edited body
1d
revised Runge Phenomena and Taylor Expansion
added 47 characters in body
1d
answered Runge Phenomena and Taylor Expansion
1d
answered Digital Roots of Square Numbers
1d
comment What is the definition of a Critical Point?
"Might" is too vague to use in definitions.
1d
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