问题


There is a single choice question about abstract algebra. Answer the question by replying A, B, C or D.
Question: Statement 1 | Every group of order 42 has a normal subgroup of order 7. Statement 2 | Every group of order 42 has a normal subgroup of order 8.
A. True, True
B. False, False
C. True, False
D. False, True
Answer:

答案

模型 模型答案 正确答案
金声玉亮2.0

C
C
deepseekr1

To analyze the statements:

**Statement 1**: Every group of order 42 has a normal subgroup of order 7.
- By Sylow's third theorem, the number of Sylow 7-subgroups \( n_7 \) must satisfy \( n_7 \equiv 1 \mod 7 \) and \( n_7 \mid 6 \). The only possible values are \( n_7 = 1 \), as \( n_7 = 6 \) leads to a contradiction due to insufficient remaining elements for Sylow 2 and 3 subgroups. Thus, there is a unique (normal) Sylow 7-subgroup. **True**.

**Statement 2**: Every group of order 42 has a normal subgroup of order 8.
- By Lagrange’s theorem, the order of a subgroup must divide the group’s order. Since 8 does not divide 42, no subgroup of order 8 can exist. **False**.

**Answer**: C. True, False
C
gpto1 C C
GPT-4o C. True, False C
llama3.1-70B-Instruct

C
C
llama3.1-405B-Instruct

C
C
DeepSeek-Coder-V2 B C
Qwen2-72B-Instruct C. True, False C
baichuan4 C. True, False C
doubao C. True, False.

By Sylow's theorems, a group of order 42 (which is 2×3×7) has a normal subgroup of order 7. But a group of order 42 does not necessarily have a normal subgroup of order 8.
C
minimax C. True, False

Explanation:
Statement 1 is true because of Sylow's theorems. A group of order 42 has order 2 * 3 * 7. By Sylow's theorems, the number of Sylow 7-subgroups (subgroups of order 7) must divide 6 and be congruent to 1 mod 7. The only number that satisfies these conditions is 1, so there is exactly one Sylow 7-subgroup, which must be normal.

Statement 2 is false because a group of order 42 does not necessarily have a normal subgroup of order 8. The order of the group is not a multiple of 8, so there is no requirement for a Sylow 2-subgroup of order 8 to exist, much less to be normal. Moreover, the number of Sylow 2-subgroups must divide 21 and be congruent to 1 mod 2, which could be 1 or 3 or 7 or 21. None of these necessarily implies a normal subgroup of order 8.
C
kimi To answer this question, we need to consider the Sylow theorems, which are a set of theorems that give information about the possible subgroups of a group given the prime factorization of the group's order.

Statement 1: Every group of order 42 has a normal subgroup of order 7.
- The order of the group is 42, which is \(2 \times 3 \times 7\).
- According to Sylow's First Theorem, there exists a Sylow 7-subgroup (a subgroup of order 7) in the group.
- By Sylow's Third Theorem, the number of Sylow 7-subgroups, denoted by \(n_7\), must divide the order of the group and be congruent to 1 modulo 7. Since 42 is not divisible by 7, \(n_7\) must be 1.
- This means there is a unique Sylow 7-subgroup, and because it is unique, it is normal in the group.

Statement 2: Every group of order 42 has a normal subgroup of order 8.
- The order of the group is still 42.
- There is no requirement that a group of order 42 must have a normal subgroup of order 8. Sylow's Third Theorem does not guarantee this.
- The number of Sylow 2-subgroups (subgroups of order 8), denoted by \(n_2\), must divide 42 and be congruent to 1 modulo 2. This means \(n_2\) could be 1, 3, 7, 21, or 41.
- If \(n_2\) is 1, then there is a unique Sylow 2-subgroup, which would be normal. However, if \(n_2\) is greater than 1, there is no guarantee that any of these subgroups are normal.

Based on the above analysis, Statement 1 is true, and Statement 2 is not necessarily true.

Answer: C. True, False
C
wenxinyiyan C

Explanation:

1. **Statement 1**:


* Consider a group $G$ of order 42.
* The number of 7-Sylow subgroups of $G$ is given by $n_7 = 1 + 7k$ for some non-negative integer $k$, and $n_7$ divides 6 (the index of the 7-Sylow subgroup in $G$).
* The only possible values of $n_7$ that satisfy these conditions are 1 and 6.
* If $n_7 = 1$, then the unique 7-Sylow subgroup is normal in $G$.
* Assume for contradiction that $n_7 = 6$. Then there are 6 distinct subgroups of order 7, each with 6 distinct non-identity elements. Since these subgroups are distinct, their non-identity elements are also distinct.
* This gives a total of $6 \times 6 = 36$ distinct non-identity elements in these subgroups.
* However, $G$ has only 42 elements, so there are only 41 non-identity elements. This is a contradiction.
* Therefore, $n_7 = 1$ and there is a unique normal subgroup of order 7 in $G$.
* **Conclusion**: Statement 1 is true.
2. **Statement 2**:


* Consider a group $G$ of order 42.
* If $G$ has a normal subgroup $H$ of order 8, then $H$ must be abelian (since all groups of order $p^2$ for a prime $p$ are abelian, and 8 = $2^3$ but we only need $2^2$ here).
* Then $G/H$ is a group of order $42/8 = 5.25$, which is not an integer.
* Therefore, $G$ cannot have a normal subgroup of order 8.
* **Conclusion**: Statement 2 is false.
C
zhipu To determine the correct answer, we need to analyze both statements based on group theory principles.

**Statement 1: Every group of order 42 has a normal subgroup of order 7.**

- The order of a group \( G \) is the number of elements in \( G \).
- By the Sylow theorems, for a group of order \( 42 = 2 \times 3 \times 7 \), we consider the Sylow \( p \)-subgroups for \( p = 2, 3, \) and \( 7 \).
- A Sylow \( 7 \)-subgroup has order \( 7 \), which is a prime number.
- The number of Sylow \( 7 \)-subgroups, denoted \( n_7 \), must divide the order of the group and be congruent to 1 modulo 7.
- Thus, \( n_7 \) must divide 6 (since \( 42/7 = 6 \)) and \( n_7 \equiv 1 \pmod{7} \).
- The only integer satisfying these conditions is \( n_7 = 1 \).
- Therefore, there is exactly one Sylow \( 7 \)-subgroup, and it must be normal.

So, Statement 1 is **True**.

**Statement 2: Every group of order 42 has a normal subgroup of order 8.**

- A subgroup of order 8 in a group of order 42 would imply the existence of elements whose orders are factors of 8.
- However, for a group of order 42, the possible orders of elements must divide 42 (which are 1, 2, 3, 6, 7, 14, 21, and 42).
- There are no elements of order 8 in a group of order 42 because 8 does not divide 42.
- Hence, it is impossible for a group of order 42 to have a subgroup of order 8.

So, Statement 2 is **False**.

Combining these results, the correct answer is:

**C. True, False**
C
gpto1 C C
deepseekv3 The correct answer is **C. True, False**.

### Explanation:
1. **Statement 1**: Every group of order 42 has a normal subgroup of order 7.
- This is **true**. By Sylow's theorems, the number of Sylow 7-subgroups \( n_7 \) must divide 6 (the index of the Sylow 7-subgroup) and satisfy \( n_7 \equiv 1 \mod 7 \). The only possibility is \( n_7 = 1 \), meaning there is a unique Sylow 7-subgroup, which is necessarily normal.

2. **Statement 2**: Every group of order 42 has a normal subgroup of order 8.
- This is **false**. The order of a subgroup must divide the order of the group. Since 8 does not divide 42, there cannot be a subgroup of order 8, let alone a normal one.

Thus, the correct answer is **C. True, False**.
C