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19h
reviewed Approve $y_{2n}, y_{2n+1}$ and $y_{3n}$ all converge. What can we say about the sequence $ y_n$?
19h
reviewed Approve Proving $T(n) = 1 + \sum_{j=0}^{n-1} T(j)$, $T(0)=1$ implies $T(n)=2^n$
Apr
21
reviewed Leave Open Common terms between two arithmetic series
Apr
21
reviewed Leave Open A proof about boundedness for continuous functions
Apr
21
reviewed Close Martingale difference sequence
Apr
21
reviewed Leave Open Why $R/AB$ is cyclic?
Apr
21
reviewed Approve Dropping the lowest number in a set lowers the mean average of the set.
Apr
21
reviewed Approve Riemann Sum proofs
Apr
12
awarded  Nice Answer
Mar
31
comment Push Down Automata
What have you tried so far? Also, do you know how to construct a PDA for $a^nb^n$? If you have one for $a^nb^n$ and one for $a^nc^n$, what can you do with that?
Mar
5
awarded  Yearling
Feb
22
comment When is matrix multiplication commutative?
Here's an example why this condition is not neccesary: Take any non-diagonalizable matrix $A$. It will always commute with the unit matrix $1$, but $A$ and $1$ are clearly not simultaneously diagonalizable.
Feb
12
comment When is matrix multiplication commutative?
It's not neccesary, AFAICT. I can't think of a counter-example right know, though.
Jan
31
awarded  Revival
Jan
22
comment $f(x) \in R[X]$ irreducible $\Rightarrow (f(x))$ ideal?
Just to make sure: Do you mean by $(f)$ the ideal generated by $f$?
Jan
11
comment Powers of $2\times 2$ matrices, such that $A^n = I$
Do you know about rotation matrices?
Dec
19
awarded  Caucus
Sep
30
awarded  Explainer
Sep
25
awarded  Nice Answer
Sep
13
comment What is a polynomially bounded function?
Your argument would be correct if, say, $2^x-1$ was actually a polynomial. But by definition, a polynomial is of the form $a_n x^n + a^{n-1} x^{n-1} + \cdots + a_0$ for some parameters $a_0, \ldots, a_n$, and $2^x-1$ is not of this form.