5. How many automorphisms does Klein's 4-group have?

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Chapter2: Second-order Linear Odes
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**Question 5: Automorphisms of Klein's 4-group**

How many automorphisms does Klein’s 4-group have?

**Explanation:**

Klein's 4-group, often denoted as \( V_4 \), is a group with four elements, typically \(\{ e, a, b, c \}\), where \( e \) is the identity element. It has the structure of a direct product of two cyclic groups of order 2. The group is abelian, with each element other than the identity having order 2.

An *automorphism* is a bijective homomorphism from a group to itself. For Klein’s 4-group, determining the number of automorphisms involves finding the number of bijective homomorphisms that map the group onto itself while preserving the group operation.

**Detailed Explanation:**

- **Structure:** The group has three elements of order 2 and an identity element. Each non-identity element generates a subgroup of order 2.
- **Automorphism Group:** The automorphism group \(\text{Aut}(V_4)\) is isomorphic to the symmetric group \( S_3 \), which is the group of all permutations of three objects. This results because each automorphism is determined by the image of the non-identity elements, which can be permuted in \( 3! = 6 \) ways.

Therefore, Klein’s 4-group has 6 automorphisms.
Transcribed Image Text:**Question 5: Automorphisms of Klein's 4-group** How many automorphisms does Klein’s 4-group have? **Explanation:** Klein's 4-group, often denoted as \( V_4 \), is a group with four elements, typically \(\{ e, a, b, c \}\), where \( e \) is the identity element. It has the structure of a direct product of two cyclic groups of order 2. The group is abelian, with each element other than the identity having order 2. An *automorphism* is a bijective homomorphism from a group to itself. For Klein’s 4-group, determining the number of automorphisms involves finding the number of bijective homomorphisms that map the group onto itself while preserving the group operation. **Detailed Explanation:** - **Structure:** The group has three elements of order 2 and an identity element. Each non-identity element generates a subgroup of order 2. - **Automorphism Group:** The automorphism group \(\text{Aut}(V_4)\) is isomorphic to the symmetric group \( S_3 \), which is the group of all permutations of three objects. This results because each automorphism is determined by the image of the non-identity elements, which can be permuted in \( 3! = 6 \) ways. Therefore, Klein’s 4-group has 6 automorphisms.
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