5. Suppose E is a finite extension of a field F and K and L are subfields of E that contain F and are normal over F. Prove that KOL is normal over F.

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**Field Theory Problem**

**Problem Statement:**
Suppose \( E \) is a finite extension of a field \( F \). Let \( K \) and \( L \) be subfields of \( E \) that contain \( F \) and are normal over \( F \). Prove that \( K \cap L \) is normal over \( F \).

**Explanation:**

In this problem, you have three fields involved: \( F \), \( E \), and the intersection \( K \cap L \). The fields \( K \) and \( L \) are subfields of \( E \), and you are given that they are both normal extensions over \( F \). The goal is to demonstrate that their intersection \( K \cap L \) also retains this property of being a normal extension over \( F \).

Things to consider:

1. **Field Extensions:** A field extension \( E \) over \( F \) is called normal if every irreducible polynomial in \( F[x] \) that has at least one root in \( E \), actually splits into linear factors in \( E \).

2. **Intersection of Fields:** The intersection \( K \cap L \) consists of all elements common to both fields \( K \) and \( L \) which are themselves subfields of \( E \).

3. **Proving Normality:** To prove that \( K \cap L \) is normal over \( F \), you need to show that any irreducible polynomial in \( F[x] \) that has a root in \( K \cap L \) splits completely into linear factors in \( K \cap L \).

This problem is an exercise in understanding and applying the concept of normal extensions in the context of field theory, a foundational area in abstract algebra and number theory.
Transcribed Image Text:Certainly! Below is a transcription suitable for an educational website: --- **Field Theory Problem** **Problem Statement:** Suppose \( E \) is a finite extension of a field \( F \). Let \( K \) and \( L \) be subfields of \( E \) that contain \( F \) and are normal over \( F \). Prove that \( K \cap L \) is normal over \( F \). **Explanation:** In this problem, you have three fields involved: \( F \), \( E \), and the intersection \( K \cap L \). The fields \( K \) and \( L \) are subfields of \( E \), and you are given that they are both normal extensions over \( F \). The goal is to demonstrate that their intersection \( K \cap L \) also retains this property of being a normal extension over \( F \). Things to consider: 1. **Field Extensions:** A field extension \( E \) over \( F \) is called normal if every irreducible polynomial in \( F[x] \) that has at least one root in \( E \), actually splits into linear factors in \( E \). 2. **Intersection of Fields:** The intersection \( K \cap L \) consists of all elements common to both fields \( K \) and \( L \) which are themselves subfields of \( E \). 3. **Proving Normality:** To prove that \( K \cap L \) is normal over \( F \), you need to show that any irreducible polynomial in \( F[x] \) that has a root in \( K \cap L \) splits completely into linear factors in \( K \cap L \). This problem is an exercise in understanding and applying the concept of normal extensions in the context of field theory, a foundational area in abstract algebra and number theory.
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