Boris Novikov's user avatar
Boris Novikov's user avatar
Boris Novikov's user avatar
Boris Novikov
  • Member for 11 years
  • Last seen more than 9 years ago
45 votes

Prove that the additive group $ℚ$ is not isomorphic with the multiplicative group $ℚ^*$.

43 votes

Why is $\frac{987654321}{123456789} = 8.0000000729?!$

24 votes
Accepted

if $ab=cd$ then $a+b+c+d $ is composite

15 votes
Accepted

Prove that $(G, \circ)$ is a group if $a\circ x = b$ and $x\circ a = b$ have unique solutions

15 votes

Good math bed-time stories for children?

14 votes
Accepted

Concept of a subring in Atiyah-Macdonald's book

13 votes

Torsion Subgroup (Just a set) for an abelian (non abelian) group.

13 votes

$G$ is Abelian if it has no element of order $2$ and $(ab)^2=(ba)^2$

12 votes
Accepted

Do Boolean rings always have a unit element?

10 votes
Accepted

Atiyah-Macdonald, Proposition 2.12, uniqueness of the tensor product.

10 votes

Groups of order 2k have a normal subgroup of order k and odd permutations

9 votes
Accepted

Let $G$ be abelian, $H$ and $K$ subgroups of orders $n$, $m$. Then G has subgroup of order $\operatorname{lcm}(n,m)$.

9 votes

Prove that $\exists a,g,h\in G\colon h=aga^{-1}, g\neq h ,gh=hg$ in a finite non-abelian group $G$.

9 votes

Ring theory reference books

9 votes
Accepted

$\lim_{n\to\infty}(\sqrt{n^2+n}-\sqrt{n^2+1})$

9 votes

solve trigonometric equation $\cos(2x) + \cos\left(x\right) -2 = 0$

9 votes

If $H_1, H_2\leq G$ are such that $H_1\cong H_2$ then $G/H_1\cong G/H_2$?

8 votes

Show that $\gcd(a,b)=\operatorname{lcm}(a,b)$ if and only if $a=b$.

8 votes

How can I find the value of $\ln( |x|)$ without using the calculator?

8 votes

Status of the classification of non-finitely generated abelian groups.

8 votes

How do I sell out with abstract algebra?

8 votes
Accepted

Where can I learn about the lattice of partitions?

8 votes

How did we know to invent homological algebra?

8 votes
Accepted

What is the mathematical foundation of Control Theory?

8 votes
Accepted

Find $S$ where $S=\sqrt[3] {5+2 \sqrt {13}}+\sqrt[3]{5-2 \sqrt {13}}$, why am I getting an imaginary number?

7 votes
Accepted

Structure theorem for finitely generated commutative $semi$groups.

7 votes

If $G$ is a finite group, $H$ is a subgroup of $G$, and there is an element of $G/H$ of order $n$, then there is an element of $G$ of order $n$

7 votes
Accepted

Questions involving two polynomials

7 votes

What can we say about the size of $HK\cap KH$ when $HK\neq KH$?

7 votes

Can we embed cancellative rings into division rings?

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