2.15. (a) Prove that GL2 (Fp) is a group. (b) Show that GL2 (Fp) is a noncommutative group for every prime p. (c) Describe GL2 (F2) completely. That is, list its elements and describe the multi- plication table. (d) How many elements are there in the group GL2(Fp)? (e) How many elements are there in the group GLn (Fp)?

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### Chapter 2: Linear Algebra - Group Theory

#### Exercise 2.15

This exercise set explores the properties and structure of the general linear group of 2x2 invertible matrices over a finite field, denoted as \( GL_2(\mathbb{F}_p) \).

**(a) Prove that \( GL_2(\mathbb{F}_p) \) is a group.**

This question requires you to demonstrate that the set of all 2x2 invertible matrices over the finite field \( \mathbb{F}_p \) satisfies the group axioms:
1. **Closure**: The product of any two invertible matrices is also invertible.
2. **Associativity**: Matrix multiplication is associative.
3. **Identity Element**: There exists an identity matrix \( I \) such that for any matrix \( A \in GL_2(\mathbb{F}_p) \), \( AI = IA = A \).
4. **Inverse Element**: Every matrix \( A \in GL_2(\mathbb{F}_p) \) has an inverse \( A^{-1} \) such that \( AA^{-1} = A^{-1}A = I \).

**(b) Show that \( GL_2(\mathbb{F}_p) \) is a noncommutative group for every prime \( p \).**

This part asks you to demonstrate that for any prime \( p \), matrix multiplication in \( GL_2(\mathbb{F}_p) \) is generally not commutative; i.e., there exist matrices \( A \) and \( B \) in \( GL_2(\mathbb{F}_p) \) such that \( AB \neq BA \).

**(c) Describe \( GL_2(\mathbb{F}_2) \) completely. That is, list its elements and describe the multiplication table.**

Here, you are asked to detail the specific elements of \( GL_2(\mathbb{F}_2) \) and provide a multiplication table, showing how every pair of elements multiplies.

**(d) How many elements are there in the group \( GL_2(\mathbb{F}_p) \)?**

This question involves counting the number of invertible 2x2 matrices over \( \mathbb{F}_p \). To solve this, you must consider
Transcribed Image Text:### Chapter 2: Linear Algebra - Group Theory #### Exercise 2.15 This exercise set explores the properties and structure of the general linear group of 2x2 invertible matrices over a finite field, denoted as \( GL_2(\mathbb{F}_p) \). **(a) Prove that \( GL_2(\mathbb{F}_p) \) is a group.** This question requires you to demonstrate that the set of all 2x2 invertible matrices over the finite field \( \mathbb{F}_p \) satisfies the group axioms: 1. **Closure**: The product of any two invertible matrices is also invertible. 2. **Associativity**: Matrix multiplication is associative. 3. **Identity Element**: There exists an identity matrix \( I \) such that for any matrix \( A \in GL_2(\mathbb{F}_p) \), \( AI = IA = A \). 4. **Inverse Element**: Every matrix \( A \in GL_2(\mathbb{F}_p) \) has an inverse \( A^{-1} \) such that \( AA^{-1} = A^{-1}A = I \). **(b) Show that \( GL_2(\mathbb{F}_p) \) is a noncommutative group for every prime \( p \).** This part asks you to demonstrate that for any prime \( p \), matrix multiplication in \( GL_2(\mathbb{F}_p) \) is generally not commutative; i.e., there exist matrices \( A \) and \( B \) in \( GL_2(\mathbb{F}_p) \) such that \( AB \neq BA \). **(c) Describe \( GL_2(\mathbb{F}_2) \) completely. That is, list its elements and describe the multiplication table.** Here, you are asked to detail the specific elements of \( GL_2(\mathbb{F}_2) \) and provide a multiplication table, showing how every pair of elements multiplies. **(d) How many elements are there in the group \( GL_2(\mathbb{F}_p) \)?** This question involves counting the number of invertible 2x2 matrices over \( \mathbb{F}_p \). To solve this, you must consider
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