User Srijan

33 votes

How to find all the maximal ideals of $\mathbb Z_n?$

answered Apr 19, 2013 at 4:25

32 votes

Describe all ring homomorphisms

answered May 4, 2013 at 9:36

18 votes

Accepted

$I-AB$ be invertible $\Leftrightarrow$ $I-BA$ is invertible

answered Apr 18, 2013 at 21:13

17 votes

Accepted

$\mathbb{Q}$ is not open, is not closed, but is the countable union of closed sets.

answered Apr 18, 2013 at 19:03

14 votes

Accepted

Condition number of a rectangular matrix

answered Apr 28, 2013 at 19:32

12 votes

Is there a non-abelian group $G$ such that $\operatorname{Aut}(G)$ is abelian?

answered May 30, 2013 at 0:56

10 votes

Accepted

How to prove $\lvert \lVert x \rVert - \lVert y \rVert \rvert \overset{\heartsuit}{\leq} \lVert x-y \rVert$?

answered May 30, 2013 at 6:50

9 votes

Accepted

Largest order of an element in a group

answered May 5, 2013 at 17:09

9 votes

Can a function be uniformly continuous on an open interval?

answered May 21, 2013 at 6:29

9 votes

Determine all subgroups of $\mathbb{R}^*$ that have finite index.

answered Apr 19, 2013 at 6:32

9 votes

Showing $\sin(\bar{z})$ is not analytic at any point of $\mathbb{C}$

answered Jun 4, 2012 at 7:00

9 votes

If a topological space is a path-connected, it is also connected. The converse fails. Can this be remedied?

answered Apr 16, 2013 at 10:52

8 votes

Proving connectedness of the $n$-sphere

answered Apr 17, 2013 at 12:45

8 votes

Why does the taylor series of $\ln (1 + x)$ only approximate it for $-1<x \le 1$?

answered Apr 18, 2013 at 15:16

8 votes

Determine all subgroups of $\mathbb{R}^*$ (nonzero reals under multiplication) of index $2$.

answered Apr 18, 2013 at 16:19

8 votes

Quotient rings of Gaussian integers $\,\Bbb Z[i]/(a+bi)\cong\Bbb Z/(a^2+b^2)\ $ if $\ (a,b)=1$

answered Apr 26, 2013 at 2:45

7 votes

Accepted

If order of the element $a^5$ is 12 can we make any guess about the order of the element $a$ in a group $G$?

answered Apr 30, 2013 at 18:45

7 votes

How can a matrix be Hermitian, unitary, and diagonal all at once?

answered May 5, 2013 at 9:43

7 votes

Is it true that $\lvert \sin z \rvert \leq 1$ for all $z\in \mathbb{C}$?

answered May 12, 2012 at 10:17

7 votes

Accepted

A group of order 105 contains a subgroup of order 35.

answered Apr 21, 2013 at 14:56

6 votes

Find all maximal ideals of $\mathbb{Z}_{540}$

answered Apr 19, 2013 at 16:58

6 votes

Every set of non-overlapping disks in the plane is at most countable?

answered Apr 18, 2013 at 21:53

6 votes

Accepted

Trace of the matrix power

answered Apr 16, 2013 at 11:06

6 votes

Type of singularities of $\frac{z}{e^z-1}$

answered May 31, 2013 at 9:15

5 votes

Accepted

Existence of a function satisfying given conditions

answered May 30, 2013 at 6:15

5 votes

Accepted

What does a linear transformation do to a vector in $\mathbb{R}^2$

answered May 3, 2017 at 10:25

5 votes

Accepted

Searching for unbounded, non-negative function $f(x)$ with roots $x_{n}\rightarrow \infty$ as $n \rightarrow \infty$

answered May 21, 2013 at 7:15

5 votes

which of the followings are positive definite:

answered May 21, 2013 at 12:57

4 votes

All group homomorphism from $ \mathbb{Z} _m $ to $\mathbb{Z}_n $

answered Apr 25, 2013 at 14:07

4 votes

For a nilpotent square matrix $A$, $I + aA$ is invertible (for scalar $a$)

answered May 2, 2017 at 8:36

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72 Answers

How to find all the maximal ideals of $\mathbb Z_n?$

Describe all ring homomorphisms

$I-AB$ be invertible $\Leftrightarrow$ $I-BA$ is invertible

$\mathbb{Q}$ is not open, is not closed, but is the countable union of closed sets.

Condition number of a rectangular matrix

Is there a non-abelian group $G$ such that $\operatorname{Aut}(G)$ is abelian?

How to prove $\lvert \lVert x \rVert - \lVert y \rVert \rvert \overset{\heartsuit}{\leq} \lVert x-y \rVert$?

Largest order of an element in a group

Can a function be uniformly continuous on an open interval?

Determine all subgroups of $\mathbb{R}^*$ that have finite index.

Showing $\sin(\bar{z})$ is not analytic at any point of $\mathbb{C}$

If a topological space is a path-connected, it is also connected. The converse fails. Can this be remedied?

Proving connectedness of the $n$-sphere

Why does the taylor series of $\ln (1 + x)$ only approximate it for $-1<x \le 1$?

Determine all subgroups of $\mathbb{R}^*$ (nonzero reals under multiplication) of index $2$.

Quotient rings of Gaussian integers $\,\Bbb Z[i]/(a+bi)\cong\Bbb Z/(a^2+b^2)\ $ if $\ (a,b)=1$

If order of the element $a^5$ is 12 can we make any guess about the order of the element $a$ in a group $G$?

How can a matrix be Hermitian, unitary, and diagonal all at once?

Is it true that $\lvert \sin z \rvert \leq 1$ for all $z\in \mathbb{C}$?

A group of order 105 contains a subgroup of order 35.

Find all maximal ideals of $\mathbb{Z}_{540}$

Every set of non-overlapping disks in the plane is at most countable?

Trace of the matrix power

Type of singularities of $\frac{z}{e^z-1}$

Existence of a function satisfying given conditions

What does a linear transformation do to a vector in $\mathbb{R}^2$

Searching for unbounded, non-negative function $f(x)$ with roots $x_{n}\rightarrow \infty$ as $n \rightarrow \infty$

which of the followings are positive definite:

All group homomorphism from $ \mathbb{Z} _m $ to $\mathbb{Z}_n $

For a nilpotent square matrix $A$, $I + aA$ is invertible (for scalar $a$)