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Sep
20
revised Presentation of a group: Show that $\langle a|a^2\rangle =\{1,a\}$.
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Sep
20
comment subspace of the Vector Space of real valued functions
You proved that $W$ is not a subspace of $\Bbb R^{\Bbb R}$. It's not a subspace of anything because $0\not\in W$.
Sep
19
revised Does $\lim_{n\to\infty}S_n \leq S$ imply that $S_n < S$?
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Sep
10
comment Is there a power of 2 that, written backward, is a power of 5?
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Sep
9
answered Prove that $\sin(x+a), \sin(x+b),\sin(x+c), \hspace{5pt} a,b,c \in \mathbb{R}$ are linearly dependent
Sep
9
comment If $P \leq G$, $Q\leq G$, are $P\cap Q$ and $P\cup Q$ subgroups of $G$?
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Sep
9
comment Tricks to Prove Union of Two Subgroups iff One is Contained in the Other - Fraleigh p. 54 - based on Exercise 5.4.5
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Aug
25
comment Proof that the set of all functions from $\mathbb N$ to $\mathbb N$ is not enumerable
@Guilherme D Look at this
Aug
25
revised Proof that the set of all functions from $\mathbb N$ to $\mathbb N$ is not enumerable
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Aug
24
comment How can I show why this equation has no complex roots?
Yes, sorry I didn't see them. The problem is that I'm not sure you can cancel out .
Aug
24
comment How can I show why this equation has no complex roots?
$$1,2,\ldots,n$$
Aug
24
comment How can I show why this equation has no complex roots?
There are more roots of $F_{n+2} = F_n$other that those of your last equation. Any root of $F_n = 0$ would be a root of $F_{n+2} = F_n$.
Aug
19
revised Finding characteristic equation of problem and solve recurrence relation
deleted 12 characters in body
Aug
16
comment Show that $\mathbb Z[x]$ and $\mathbb Q_{>0}$ are isomorphic
This question has been already asked
Aug
12
revised If $AB = I$ then $BA = I$
Tuning this into a correct argument.
Aug
8
revised How prove that $\max(|f(1)|,|f(2)|,|f(3)|,|f(4)|)\geq \frac{1}{2}$ if $f(x) = \cos(Ax)+\cos(Bx)$?
edited title
Aug
6
revised Proof for '$AB = I$ then $BA = I$' without Motivation?
Formatting.
Aug
6
reviewed Close Simplifying this sigma notation
Aug
6
revised Show that a finite group with certain automorphism is abelian
english
Aug
6
comment How to prove that $\det\left[\pmatrix{u_1 & v_1\\ u_2 & v_2\\ u_3 & v_3}\pmatrix{s_1 & s_2 & s_3\\ t_1 & t_2 & t_3}\right]=0$?
@Nishant you're right, let me correct myself: Let $A$ be a $m\times n$ matrix and $B$ be a $n\times m$ matrix. If $n\lt m$ then $AB$ is not invertible.