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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Showing that $(\mathbb{R} \setminus \{ 0 \}, \, \times) \not \cong (\mathbb{C} \setminus \{ 0 \}, \, \times)$

I'm trying to show that $(\mathbb{R} \setminus \{ 0 \}, \, \times) \not \cong (\mathbb{C} \setminus \{ 0 \}, \, \times)$ as follows: note that there exists an element (namely $i$) in $\mathbb{C} \setminus \{ 0 \}$ that has order $4$, but no element…
Ryan
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Power of prime ideal

I am beginner in algebra. I want to know if every power of a prime ideal is a principal ideal. Is the statement correct or is there a counterexample?
Vahid
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If $p$ is prime and $|G|<\infty$ such that every element has order a power of $p$ then $G$ is a $p$-group?

can anyone help me with following exercise from Rotmann's Advanced Modern Algebra book: Exercise: Prove that if $p$ is prime and $G$ is a finite group such that every element has order a power of $p$ then $G$ is a $p$-group. Hint: Use Cauchy's…
PtF
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Connected points problem for $\mathbb Q$

Two points in $\mathbb Q$ are called connected, if their euclidean distance is exactly $1$. You are now allowed to also jump from any point in $\mathbb Q^n$ to another, if they are connected in $\mathbb Q^n$. The question now is: What is the…
Imago
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Find eight elements in $S_6$ that commute with $(12)(34)(56)$

This is a homework problem and I'm having trouble just getting a basic understanding. I understand that $S_6$ is a symmetric group of degree $6$. I'm not sure how to start looking for elements.
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Calculate $g^2, g^3, f^2$

Everyone. I am not sure how to start this problem. If anyone can show me a step by step process with an explanation I would appreciate it. If $S= \{x_1,x_2,x_3,x_4\}$, let $f,g\in S_4$ be defined by: $$f:x_1\to x_2, x_2\to x_3, x_3\to x_4, x_4\to…
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Question about field and ED

Let $R$ be commutative ring and $R[x]$ be ring of polynomial in one variable. True/false "If $R$ is field then $R[x]$ is an ED." I think the above statement is true from result, "If $R$ is commutative ring such that polynomial ring $R[x]$ is ED then…
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On finding the number of homomorphisms from $G$ to $G_1\oplus \cdots \oplus G_n$

How shall I establish that the number of homomorphisms from the group $G$ to $G_1\oplus G_2\oplus \cdots G_n$ is same as $h_1h_2\cdots h_n$ where $h_i$ is the number of homomorphisms from $G$ to $G_i$ ? Here $G, G_1, G_2, \cdots, G_n$ are all…
KON3
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prove that either $f=I_{\mathbb Z}$ is the identity function or $f(x)=0, \forall x \in \mathbb Z$.

Let $f:\mathbb Z \rightarrow \mathbb Z$ such that $f(x+y)=f(x)+f(y), \forall x,y \in \mathbb Z$ and $f(xy)=f(x)f(y), \forall x,y \in \mathbb Z$. I need to prove that either $f=I_{\mathbb Z}$ is the identity function or $f(x)=0, \forall x \in \mathbb…
Walter r
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Is there a criterion for such black/white stone game?

Black and white stones arranged as $m$ row and $n$ columns. At each move, you could choose either one row or one column, and reverse each stone's color -- turn white stones to black, and black stones to white. To determine if the beginning…
athos
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Irreduciblility of $x^3 + 9x + 6 $ in $\mathbb{Q}[x]$

I am trying to prove the irreducibility of $x^3 + 9x + 6 $ in $\mathbb{Q}[x]$ without using Eisenstein's criterion. What I have done is -- Let assume it is reducible in $\mathbb{Q}[x]$, then it can be written as $$x^3 + 9x + 6 = (a'x^2 + b'x+…
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Prove that $R[x]/(I,f)$ is isomorphic to $(R/I)[x]/(f')$, where $f'$ is $f$ in $R/I$.

Prove that $R[x]/(I,f)$ is isomorphic to $(R/I)[x]/(f')$, where $f'$ is $f$ in $R/I$. Attempt: I know how to prove $R[x]/(I) \cong (R/I)[x]$ using the first isomorphism theorem and the homomorphism that sends $f \in R[x]$ to $f' \in…
clueless
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How do I prove this reducibility result about biquadratic extensions?

Possible Duplicate: Are quartic minimal polynomials over $\mathbb{Q}$ always reducible over $\mathbb{F}_p$? This question was originally a homework problem for an algebra course, but the professor took it off the homework once he realized it was…
MathTeacher
  • 1,559
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Quotient ring of $\mathbb{R}[x]$

I have learned in my class that quotient ring of $\mathbb{R}[x] / (x^2 + 1) \cong \mathbb{C}$. Just from curiosity, I was interested in knowing if $$ \mathbb{R}[x] / (x^2 + ax + b) \cong \mathbb{C} $$ holds for any $a,b \in \mathbb{R}$? Thanks!
Tom Mosher
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Prove that every rational number $r$ can be written as $r=\frac{p}{q}$, where $p$, $q$ $\in \mathbb{Z}$

Prove that every rational number $r$ can be written as $r=\frac{p}{q}$, where $p$, $q$ $\in \mathbb{Z}$, $q \gt 0$ and $p$, $q$ are relatively prime. Moreover the integers $p$ and $q$ are uniquely determined by $r$. My try: Let $R$ be a relation on…
tattwamasi amrutam
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