Abstract Algebra: Rings & Ideals Quiz
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Abstract Algebra: Rings & Ideals Quiz

Created by
@ChivalrousSard7112

Questions and Answers

What is a ring (with unity)?

A set with operations * and + such that (R, +) is an abelian group, there exists a 1 ∈ R such that 1 * a = a * 1 = a, a * (b * c) = (a * b) * c, and a * (b + c) = a * b + a * c, (b + c) * a = b * a + c * a.

A ring is commutative if a * b = b * a.

True

What are some examples of commutative rings?

Z, Z ln Z, IR, R[x], Q.

What is a zero divisor?

<p>An element a ≠ 0 in R such that ab = 0 for some b ≠ 0 in R.</p> Signup and view all the answers

R is an integral domain if it is commutative and has no zero divisors.

<p>True</p> Signup and view all the answers

R is a field if it is commutative and every non-zero element is invertible.

<p>True</p> Signup and view all the answers

What are some examples of fields?

<p>Q, IR, Z/pZ for prime p.</p> Signup and view all the answers

What is a subring?

<p>A set S ⊆ R such that 1 ∈ S, (S, +) is a subgroup of (R, +), and a, b ∈ S implies ab ∈ S.</p> Signup and view all the answers

What is an ideal?

<p>A set I ⊆ R such that (I, +) is a subgroup of (R, +) and for x ∈ I, r ∈ R, it holds that r * x ∈ I and x * r ∈ I.</p> Signup and view all the answers

What are some examples of ideals?

<p>nZ' ⊆ Z', principal ideal = {rx : r ∈ R} in a commutative ring R.</p> Signup and view all the answers

An ideal I ⊆ R is prime in a commutative ring R if ab ∈ I implies a ∈ I or b ∈ I.

<p>True</p> Signup and view all the answers

What are examples of an ideal being prime in a commutative ring?

<p>pZ ∈ Z for prime p, ⊆ F[x] for g(x) irreducible.</p> Signup and view all the answers

What is a (unital) ring homomorphism?

<p>A map f: R → S such that f(1) = 1, f(a + b) = f(a) + f(b), and f(ab) = f(a) f(b).</p> Signup and view all the answers

F is an isomorphism if it is also bijective.

<p>True</p> Signup and view all the answers

What is the kernel of f?

<p>Ker(f) = {a ∈ R : f(a) = 0}.</p> Signup and view all the answers

What is the characteristic of R?

<p>The smallest n such that 1 + 1 + ... + 1 = 0 (n times).</p> Signup and view all the answers

If r ∈ R is a zero divisor, then r is not invertible.

<p>True</p> Signup and view all the answers

If f: R → S is a homomorphism, then Ker(f) is an ideal.

<p>True</p> Signup and view all the answers

If I ⊆ R is an ideal, what is R/I?

<p>R/I = {I + a : a ∈ R} is a ring with structure defined through operations.</p> Signup and view all the answers

What is the Fundamental Homomorphism Theorem (FHT)?

<p>If f: R → S is a surjective homomorphism, then R/Ker(f) ≅ S.</p> Signup and view all the answers

I ⊆ R is a prime ideal if and only if R/I is an integral domain.

<p>True</p> Signup and view all the answers

For any ring, what is the unique homomorphism?

<p>Z → R with Kernel char(R) Z.</p> Signup and view all the answers

Every ideal in Z is principal.

<p>True</p> Signup and view all the answers

Every ideal in F[x] is principal for a field F.

<p>True</p> Signup and view all the answers

Both Z and F[X] have division algorithms.

<p>True</p> Signup and view all the answers

What is the Rational Root Test?

<p>f(x) = a₀ + ... + aₙ X^n ∈ Z[X] implies s I a₀ and t | aₙ for the root to exist.</p> Signup and view all the answers

What is Einstein's criterion?

<p>f(x) = a₀ + ... + aₙ X^n ∈ Z[X] has prime p such that p | aᵢ for 0 ≤ i ≤ n-1, pX aₙ, and p² | a₀ indicates that f(x) is irreducible in Q[x].</p> Signup and view all the answers

What is a group?

<p>A set G with operation * such that a * (b * c) = (a * b) * c, e ∈ G such that e * g = g * e = g, and for any g ∈ G, g⁻¹ ∈ G such that g * g⁻¹ = g⁻¹ * g = e.</p> Signup and view all the answers

What are examples of a group?

<p>Z, Z^1 / nZ, S_n, D_n, A_n.</p> Signup and view all the answers

A group is abelian if a * b = b * a.

<p>True</p> Signup and view all the answers

What is a subgroup?

<p>A subset H of G such that H ≠ ∅, a, b ∈ H implies ab ∈ H, and a ∈ H implies a⁻¹ ∈ H.</p> Signup and view all the answers

What are some examples of a subgroup?

<p>The cyclic subgroup {gⁿ : n ∈ Z} generated by g ∈ G, A_n ⊆ S_n.</p> Signup and view all the answers

What is the order of g ∈ G?

<p>The smallest n ≥ 1 such that g^n = e.</p> Signup and view all the answers

G is cyclic if G = {g^n : n ∈ Z} for some g ∈ G.

<p>True</p> Signup and view all the answers

What is a homomorphism between groups?

<p>A map f: G → H of groups such that f(ab) = f(a) f(b).</p> Signup and view all the answers

F: G → H is an isomorphism if it is also bijective.

<p>True</p> Signup and view all the answers

What are some examples of isomorphisms?

<p>S_3 ≅ D_3, Z / 2Z * Z / 3Z ≅ Z / 6Z.</p> Signup and view all the answers

What is the kernel of a homomorphism?

<p>Ker(f) = {g ∈ G : f(g) = e}.</p> Signup and view all the answers

Study Notes

Rings

  • A ring (with unity) consists of a set with operations * and + where (R, +) is an abelian group and includes multiplicative identity 1.
  • Operations follow distributive properties: a * (b + c) = ab + ac and (b + c)a = ba + c*a.
  • A ring is commutative if a * b = b * a for all a, b in R.

Types of Rings

  • Examples of commutative rings include:
    • Z (integers)
    • Z ln Z
    • IR (real numbers)
    • R[x] (polynomials with real coefficients)
    • Q (rational numbers)
  • A zero divisor is a non-zero element a in R such that there's a non-zero b in R with ab = 0.
  • An integral domain is a commutative ring without zero divisors.

Fields

  • A field is a commutative ring where every non-zero element has a multiplicative inverse.
  • Examples of fields include:
    • Q (rationals)
    • IR (reals)
    • Z/pZ for prime p.

Subrings and Ideals

  • A subring S of R satisfies:
    • Contains unity (1 ∈ S).
    • (S, +) is a subgroup of (R, +).
    • For a, b in S, their product ab is also in S.
  • An ideal I of R is defined by:
    • (I, +) being a subgroup.
    • For x ∈ I, r ∈ R, both rx and xr belong to I.

Prime Ideals

  • Ideal I in a commutative ring R is prime if ab ∈ I implies a ∈ I or b ∈ I.
  • Examples of prime ideals:
    • pZ in Z for a prime p.
    • Irreducible polynomials in F[x].

Homomorphisms

  • A (unital) ring homomorphism f: R → S includes:
    • f(1) = 1.
    • f(a + b) = f(a) + f(b).
    • f(ab) = f(a)f(b).
  • Isomorphism exists if the homomorphism is bijective.
  • The kernel of f, Ker(f), consists of elements in R mapped to the zero element in S.

Additional Concepts

  • The characteristic of R is the smallest n such that adding 1 n times equals 0.
  • For any ring, a unique homomorphism exists from Z to R with Kernel char(R)Z.
  • Every ideal in Z and F[x] is principal (generated by a single element).
  • Fundamental Homomorphism Theorem states R/Ker(f) ≅ S for a surjective homomorphism f.

Groups

  • A group G has an operation * satisfying:
    • Associativity: a * (b * c) = (a * b) * c.
    • There exists an identity element e such that e * g = g for all g in G.
    • Each g has an inverse g^(-1) such that g * g^(-1) = e.
  • A group is abelian if a * b = b * a, and examples include Z and S_n (symmetric groups).

Subgroups and Orders

  • A subgroup H of G must satisfy:
    • H is non-empty.
    • For a, b in H, the product ab is in H.
    • If a is in H, then the inverse a^(-1) is also in H.
  • The order of g in G is the smallest positive integer n such that g^n equals the identity.

Isomorphisms and Kernels

  • A map f: G → H is a homomorphism if f(ab) = f(a)f(b).
  • The kernel of a homomorphism f: G → H is Ker(f) = { g in G | f(g) = e }.

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Description

Test your understanding of rings and ideals in abstract algebra with this quiz. It covers definitions, properties, and examples of rings, including communicative rings. Ideal for students seeking to reinforce their learning in this essential area of mathematics.

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