Questions tagged [abstract-algebra]

For questions about monoids, groups, rings, modules, fields, vector spaces, algebras over fields, various types of lattices, and other such algebraic objects. Associate with related tags like [group-theory], [ring-theory], [modules], etc. as necessary to clarify which topic of abstract algebra is most related to your question and help other users when searching.

Abstract algebra is the study of algebraic objects, i.e. sets endowed with one or more operations on the elements of those sets. In particular, the study of abstract algebra considers the algebraic structures and properties of which such operations induce. It can be considered as the generalization of the study of the algebraic structure of the integers and real numbers (arithmetic), or the study of matrices and vector spaces (linear algebra).

Some algebraic objects are monoids, groups, rings, fields, vector spaces, modules, algebras, and categories, among many other less prominent objects.

Examples

  1. The set of non-negative integers $\mathbb{N} = \{0,1,2,3,\dotsc\}$ is a monoid under the operation $+$.

  2. The integers $\mathbb{Z} = \{\dotsc,-1,0,1,\dotsc\}$ under the binary operation of $+$ form a group.

  3. Furthermore, $\mathbb{Z}$ has the structure of a ring when you consider it as being equipped with both addition and multiplication.

  4. The real numbers $\mathbb{R}$ with their usual addition and multiplication form a field.

  5. The set of $n\times n$ matrices with entries in $\mathbb{R}$ with matrix addition and multiplication form a ring.

  6. The set of $1\times n$ vectors over the real numbers, with vector addition, and multiplication by elements of the $n\times n$ real matrices on the right are an example of a module for the ring of matrices.

In addition to studying the objects themselves, abstract algebra considers homomorphisms between the objects and various constructions and tools, which are useful for studying the objects.

85022 questions
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Why can a torsion-free abelian group be considered as a $\mathbb{Q}$ vector space?

Why can a torsion-free abelian group $A$ be considered as a $\mathbb{Q}$ vector space? The author in the text I am reading says we can view $A$ as a $\mathbb{Q}$ vector space due to the embedding $A \hookrightarrow A \otimes_{\mathbb{Z}}…
user93826
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Show that in any finite field, there exists a non-trivial solution for $x^2 + y^2 + z^2 + w^2 = 0$.

Show that in any finite field, there exists a non-trivial solution for $x^2 + y^2 + z^2 + w^2 = 0$. I have shown it for finite fields of cardinality $q$, when $4$ divides $q-1$ and when $q-1$ is odd. In such finite fields, $-1$ has a square root.…
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Prove that $M_n(\mathbb{Z})$ is torsion-free.

Suppose $M_n(\mathbb{Z})$ is a matrix ring with integer entries. Prove that $M_n(\mathbb{Z})$ is torsion-free. My attempt: Let $A \in Tor(M_n(\mathbb{Z}))$. Then there exists a non-zero integer such that $rA=0$, where $o$ here denotes zero matrix.…
Idonknow
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Prove that $M/Tor(M) $ is torsion-free.

Suppose $M$ is an $R$-module where $R$ is an integral domain.Define $Tor(M)$ be the set containing torsion elements of $M$. Prove that $M/Tor(M) $ is torsion-free. I have manage to prove that $Tor(M)$ is a submodule of $M$. Then my aim is to prove…
Idonknow
  • 15,643
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Associative and Commutative operations

After I got the answer here, Is multiplication the only operation that satisfies the associative, commutative and distributive law? I got to wonder how many and different operations can satisfy both associative and commutative law over rational…
KH Kim
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Is multiplication the only operation that satisfies the associative, commutative and distributive law?

I am curious whether in real numbers, the multiplication as we know it is the only operation that is distributive over addition and associative and commutative? I heard it is. But I am not sure and is there any way to prove it? Since the comments…
KH Kim
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Let $G = \langle g \rangle$ be a cyclic group of order $n = 480 = 2^5 \cdot 3^1 \cdot 5^1$.

Let $$G = \langle g \rangle$$ be a cyclic group of order $$n = 480 = 2^5 \cdot 3^1 \cdot 5^1$$, $H$ is a subgroup of $G$, and $m$ is the smallest natural number for which $g^m \in H$. Determine for which natural numbers $m$ the following conditions…
mpavlov23
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What is a 2-sided inverse?

The text says: For every permutation $\sigma$ there is a 2-sided inverse function $\sigma^{-1}: \Omega \to \Omega$ satisfying $\sigma \circ \sigma^{-1} = 1$. So I am wondering - what is the 2-sided inverse function...?
Tumbleweed
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$\mathbb{Z} \times \mathbb{Z}$ is cyclic.

Proof $\mathbb{Z} \times \mathbb{Z}$ is cyclic. My intuition is that there are four generators in $\mathbb{Z} \times \mathbb{Z}: 1 \times 1, 1 \times -1, -1 \times 1, -1 \times -1$. And the group they generated are $(z,z)$ or $(z,-z)$, rather than…
Tumbleweed
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If $a\equiv b \ \mathrm{mod}(n)$ and $m|n$, then $a\equiv b \ \mathrm{mod}(m)$.

Is this correct: If $a\equiv b \ \mathrm{mod}(n)$ and $m|n$, then $a\equiv b \ \mathrm{mod}(m)$. Let $a=q_{1}n+r$, $b=q_{2}n+r$ and $n=mc$. Then we have \begin{align*} \frac{q_{1}mc+r -(q_{2}mc+r)}{mc}=\frac{q_{1}m+r…
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Finding a ring homomorphism...

Find a ring $R$ and an explicit, onto ring homomorphism $f: \Bbb Z[x] \rightarrow R$ s.t. there is an element $a \in R$ s.t. $5a=1$. I was thinking use $R=\Bbb Z/4 \Bbb Z$ and sending the polynomial's constant term $a_0$ to $a_0$ $mod4$. This is…
Johnny Apple
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Determining $\mathrm{Gal}(L/F_5)$ of polynomial

Let $p(x):=x^4-2x^2-2 \in F_5[x]$. I am trying to find $\mathrm{Gal}(L/F_5)$, where $L$ is the splitting field of $p$ over $F_5$. My approach: So the first thing would be to prove that, $p$ is irreducible over $F_5$. But as far as I know because the…
wanymose
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$\begin{bmatrix} a & b \\ 0 & 1 \end{bmatrix}$ where $a \in (\mathbb{Z}/p)^*$ and $b \in \mathbb{Z}/p$. Describe all normal subgroups of $G$.

I'm trying to solve the following problem: Let $G$ be the group of matrices of the form $$\begin{bmatrix} a & b \\ 0 & 1 \end{bmatrix}$$ where $a \in (\mathbb{Z}/p)^*$ and $b \in \mathbb{Z}/p$. Describe all normal subgroups of $G$. My…
Math_Day
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Integral domain of order 4

Prove that there is no integral domain of order 4. Note: Trying with a contradiction.But without any results!
UNM
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Find the smallest $n$ with $(113^{13})^n \equiv 113 \bmod 155$

Find the smallest $n$ with $(113^{13})^n \equiv 113 \bmod 155$ My thoughts: Since the multiplicative ring $\mathbb{Z}_{155}$ has $155$ elements, then $a^{155}= 1$ for all $a \in \mathbb{Z}$ Hence $113^{155} \equiv 1 \bmod 155$ Then I noticed that…