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.

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Check the class equation for $\Bbb{GL}_2(\Bbb{F}_3)$

Let $G:= \Bbb{GL}_2(\Bbb{F}_3)$ be the finite group of order $48$ of invertible matrices over $\Bbb{F}_3$. Determine the center $Z(G)$, representatives $x_1,\dots,x_n$ of the conjugacy class of non central elements and the orders…
Bman72
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Isomorphism and cyclic modules

Prove that $M$ is a cyclic $R$-module if and only if exists a left ideal $I\subset R$ such that $M \simeq R/I$. I'm not sure how to even start this proof. I've been told that I could use an annhilator set to prove this, but I don't see the…
Cure
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Existence of finite, non-associative group-like structures

Do there exist sets $G$ with a composition such that $G$ is finite. There is a two-sided identity element $e\in G$ such that $eg = ge = g$ for all $g\in G$. Each $g\in G$ has a unique two-sided inverse $g^{-1}$ with $gg^{-1} = g^{-1} g = e$. For…
Gaussler
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Proof, that $(\mathbb R×\mathbb R;+,*) $ is a ring, but not a field

How do I prove, that $(\mathbb R×\mathbb R;+,*) $ is a ring, but not a field, where the $+$ and $*$ operations are: $(a,b)+(c,d):=(a+c,b+d)$ and $(a,b)*(c,d):=(ac,bd)$? For the solution: so I would have to first show, that $(\mathbb R×\mathbb…
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Are these about determinant true for commutative rings?

In my text, there was only given proofs for commutative ring with unity, then I found that the same arguments work for just commutative ring by some tricks. Here are what I have proven: Let $R$ be a commutative ring (Not necessarily with unity) Let…
Rubertos
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Are irreducible matrix algebra neccesarily simple?

In more detail, let $F$ be any field and $A$ a set of matrices, $F\cdot Id_n \subseteq A\subseteq GL_n(F)$, closed under addition and product, which is irreducible: If $\{0\}\subsetneq V \subsetneq F^n$, then $V$ is not $A$-invariant. Does it follow…
Doron
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Prove $g^2 = e$ if there is a subgroup of index 2 that does not contain $g$ for every $g \in G$.

I'm having some trouble with this question from a practice exam. Let $G$ be finite group. Suppose for every $g \in G$ other than the identity element $e$, there is a subgroup $H \subset G$ of index $2$ that does not contain $g$. Show that $g^2 = e$…
ppham27
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The Klein 4-group vs. the integers modulo 4

Let $(V,٭)$ be a group where $V=\{a,b,c,d\}$. $(V,٭)$ has the property that every element is an inverse of itself, so $V$ is called the $V$ group or the "Klein 4 group". I would like to know whether $(V,٭)$ is isomorphic to…
neema
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An integral domain with the factorization property and gcd for every two elements is a UFD

Theorem 0.6.1 of Roman's book Field Theory says: Let $R$ be an integral domain for which the factorization property holds (factorization property means that every non zero non unit can be written as a product of irreducibles). The following…
Amr
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Isomorphism of a quotient group using the stabilizer

It seems that $G_s$ need not be normal to have an isomorphism ($G_s$ and $O_s$the are stabilizer and orbit of a group action): $G/G_s \cong O_s$ First, is this accurate? Then I was wondering how this reconciles with the First Isomorphism Theorem…
user12802
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Prove that the kernel of a homomorphism is a principal ideal

RG is a group ring and R is a ring. Let $f:RG\rightarrow R$ be a homomorphism such that $f(\sum r_ig_i) = \sum r_i$ . Prove that the kernel of $f$ is a principal ideal.
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What does this factor space $\mathcal P/ \mathcal C$ look like?

Let $\mathcal P$ be the associative algebra consisting of real polynomials on the variable $x$. Set $\mathcal C$ to be the ideal of $\mathcal P $ generated by $x^2+1 $. Why does $\mathcal C$ consist of polynomials of the form $f(x)(x^2+1)g(x)$? (And…
Mussé Redi
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$\frac{1+\sqrt{m}}{2}; (19)^{1/3}$ are algebraic integral

This question is from a very old exercise sheet, I do not know what the notation $\mathbb{Z}_{\mathbb{C}}$ means: $1\equiv 1 \mod 4 $ in $\mathbb{Z}$. Show that $\frac{1+\sqrt{m}}{2} \in \mathbb{Z}_{\mathbb{C}}$ 2. Let $a= (19)^{1/3}$. Show that…
VVV
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Containment of Cyclotomic Extensions

Prove that for positive integers $d$ and $n$, the containment $\mathbb{Q}(\zeta_d) \subseteq \mathbb{Q}(\zeta_n)$ holds iff $d|n$. I have the reverse direction. Can someone give me a hint on how to prove the forward direction?
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Describe the Galois Group of a field extension

I'm struggling to understand the basics of Galois theory. One of the things I don't understand is how to actually derive automorphisms of a field extension. Let's say you had a simple problem: $x^2-3$ over $\mathbb{Q}$ has splitting field…
Roger
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