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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Is $\langle \mathbb{R}^\ast, \ast \rangle$ Where $\mathbb{R}^\ast$ Are the Real Numbers Except $0$ and $a \ast b = |a|b$ a Group?

Going by the definition of a group, that being that: For all $a,b \in G$, $a \ast b \in G$. For all $a,b,c \in G$, $a \ast (b \ast c) = (a \ast b) \ast c$. There exists an element $e$ such that for all $a \in G$, $a \ast e = e \ast a = a$. There…
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Monoids with only one-sided inverses

I'm solving an exercise in Artin that asks for a proof that that an element $a$ can have either a left or right inverse, but not be invertible. The problem comes before he has defined the notion of a group, so it seems that I only need a…
John P.
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If $G$ is a group of order 12 with conjugacy class of order 4. Show that $G$ has trivial center

Let $G$ be a group of order 12. Show that if $G$ contains a conjugacy class of order 4, the center of $G$ is $\lbrace 1\rbrace$. So I got most of the proof but get stuck at a certain point. By the counting formula, I got that the order of the…
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Order of an element in $U_n$

What are the order $6$ element in $U_7$? I guess all the members are of order 6 as they are prime to 7. $U_7$ is cyclic and $\lambda (7)= 6$, where $\lambda$ is the Carmichaeal function. So $a^6 = 1, \forall a \in U_7$. Is this a correct reason? And…
Sankha
  • 1,405
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Action of module automorphism group

It can be proven that for any vector space $V$ the action of $\mathrm{GL}(V)$ on $V \setminus \{0\}$ is transitive, and its stabilizer is $U^* \rtimes GL(U)$, where $U$ is a complement to the subspace spanned by some non-zero vector from $V$. The…
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Showing a polynomial does not belong to an ideal in $k[x,y,z]$

Consider the ring of polynomials $k[x,y,z]$, $k$ a field. Why is it clear that $x \not \in (x^{2},xz,z^{2},xy-z^{2})$ ? I mean, how do we show this rigorously? so assume it belongs, then: $x = f(x,y,z)x^{2} + g(x,y,z)xz + h(x,y,z)z^{2} +…
user9
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I have two Abstract Algebra Problems

I have a conjecture and I can't seem to find a counterexample, but I think it is false: Let $G$ be an abelian group. If $\{a_1, a_2, \dots , a_n\}$ is a minimal generating set for $G$ and for each $a_k$, $|a_k| = d_k \in \mathbb{Z}$, then each $g…
Mason
  • 10,415
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Counting the number of isomorphism types of abelian groups of order 2000

Number of isomorphism abelian groups of order 2000? $2000 = 2^4 5^3$, and the non-isomorphic groups is just $4\times 3$.
ryan
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Finite Field extensions of same degree need not be isomorphic as Fields.

Let $F$ be a Field with $\mathrm{char}(F) > 0$. $E_1$ and $E_2$ are finite extensions of $F$ of same degree. Prove that $E_1$ and $E_2$ may not be isomorphic. In Fields of characteristic zero, I get the obvious counter example namely…
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Let $F$ be a field. Find all prime and maximal ideals of $F[x]$.

Let $F$ be a field. Find all prime and maximal ideals of $F[x]$. I have no idea on how to start this question. I try to use the theorem that '$F[x]/I$ is a field $\Leftrightarrow$ $I$ is a maximal ideal $\Rightarrow$ I is a prime ideal'. But I…
Idonknow
  • 15,643
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How to show a group is infinite and non-commutative given the presentation?

I am trying to show that a group defined by the generators $a$, $b$, $c$, and $d$ and relations $adb=b^2a$, $a^3=c$, $b^2=c$, and $d^2=c$ is infinite and non-commutative. I'm not really sure how to start on this problem- am I meant to assume that…
Sarah
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Did I define a field correctly?

Let $F$ be a set, $\forall a, b, c \in F$, with two binary operations, addition and multiplication, defined on $F$, i.e. $(F, +, \times )$. Then $F$ is a field iff the following axioms hold: Closure: 1.1. Addition: $\forall a,b \in F, \exists a + b…
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Let $N$ be a normal subgroup of $G$, is $N/[N,N]\cong N/[G,G]$ true?

Here $[G,G]$ denotes the commutator, i.e., the least subgroup of $G$ containing $\{xyx^{-1}y^{-1}:x,y\in G\}$. For convention, let $\tilde G$ denote the group $G/[G,G]$. This question comes from the following theorem: Let $N$ be a normal subgroup…
Shana
  • 713
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Why the group $(\mathbb{Q}[x],+)$ is not isomorphic to $(\mathbb{Z}[x],+)$ or even $(\mathbb{Q},+)$?

I have been asked the question "Why is the group $(\mathbb{Q}[x],+)$ not isomorphic to $(\mathbb{Z}[x],+)$ or even $(\mathbb{Q},+)$?" . I will be thankful for any help. :)
Mikasa
  • 67,374
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Is $\langle x^2-x-1 \rangle$ a maximal ideal of $\mathbb{Z}[x]$?

I have to prove that $$\langle x^2-x-1 \rangle \text{ is not a maximal ideal of } \mathbb{Z}[x].$$ My attempt: I am not that much familiar with field theory but i know that an ideal $I$ is maximal over a commutative ring $R$ iff…
TheStudent
  • 1,054