Chapter 8: Problem 29
Find a generator of the indicated ideals in the indicated rings. $$ \left\langle x^{2}-5 x+6\right) \cap\left\langle x^{2}-3 x+2\right\rangle \quad \text { in } Q[x] $$
Short Answer
Expert verified
The generator is \( x-2 \).
Step by step solution
01
Understanding the Problem
We are asked to find a generator for the intersection of two ideals in the polynomial ring \( \mathbb{Q}[x] \). The ideals are \( \langle x^2 - 5x + 6 \rangle \) and \( \langle x^2 - 3x + 2 \rangle \).
02
Factor the Polynomials
First, factor the polynomials to find their roots. \( x^2 - 5x + 6 = (x-2)(x-3) \) and \( x^2 - 3x + 2 = (x-1)(x-2) \).
03
Common Divisor of the Ideals
The intersection of the ideals is generated by the polynomial whose roots are the common roots of \( (x-2)(x-3) \) and \( (x-1)(x-2) \). The roots of \( (x-2) \) are in both factorizations.
04
Construct the Generator
The generator is \( x-2 \) because \( x-2 \) is the common factor of both polynomials. Hence, the intersection of the two ideals is generated by \( x-2 \).
05
Verify the Solution
Verify that \( x-2 \) is indeed in both ideals. Since \( x-2 \) divides both \( x^2 - 5x + 6 \) and \( x^2 - 3x + 2 \), it will be a generator for their intersection.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Polynomial Ring
A Polynomial Ring, typically denoted as \( \mathbb{Q}[x] \) in our example, consists of polynomials with coefficients from the set of rational numbers, \( \mathbb{Q} \). Let's break it down further:
- Polynomials: These are mathematical expressions involving sums of powers of a variable, usually \( x \), with coefficients that are numbers from the chosen set.
- Rational Coefficients: In \( \mathbb{Q}[x] \), every coefficient is a rational number, meaning that it can be expressed as a fraction of integers.
- Operations: Within a polynomial ring, you can add, subtract, and multiply polynomials, adhering to the usual rules of algebra.
Ideal Intersection
An Ideal Intersection involves finding a common generator such that it belongs to multiple ideals within a polynomial ring. In simpler terms, this involves identifying a polynomial that can "fit" into each of the given polynomial expressions seamlessly.
- Definition of Ideal: An ideal in a ring is a set of elements where the product of any element of the ring with any element in the set is still within the set.
- Intersection of Ideals: This concept involves finding polynomials that are solutions (or generators) common to all ideals under consideration.
- Generator of Intersection: The task in our problem was to find such a polynomial which fits perfectly in both ideals given.
Polynomial Factorization
Polynomial Factorization is the process of expressing a polynomial as a product of simpler polynomials. This technique is crucial in understanding and solving our exercise.
- Why Factor Polynomials: Finding factors helps in problem-solving by identifying roots and simplifies expressions for further operations such as division and intersection of ideals.
- Step-by-Step Factorization: Our polynomials were \( x^2 - 5x + 6 \) and \( x^2 - 3x + 2 \).
- The first polynomial factored to \( (x-2)(x-3) \), indicating its roots are \( x=2 \) and \( x=3 \).
- The second polynomial factored to \( (x-1)(x-2) \), showing its roots as \( x=1 \) and \( x=2 \).
- Application in Ideal Intersection: By examining the factors, \( x-2 \) emerged as the common root. Hence, \( x-2 \) became the generator for the intersection, as it divides both initial polynomials.