Chapter 6: Problem 39
Show that \(\mathbb{Q}^{*}\) is not finitely generated.
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Chapter 6: Problem 39
Show that \(\mathbb{Q}^{*}\) is not finitely generated.
These are the key concepts you need to understand to accurately answer the question.
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Let \(\star\) be a binary operation on a non-empty, finite set \(G\). Assume that \(\star\) is associative, commutative, and satisfies the cancellation law: \(a \star b=a \star c\) implies \(b=c\). Show that \(G\) under \(\star\) forms an abelian group.
Let \(\rho: G \rightarrow G^{\prime}\) be a group homomorphism. Let \(H\) be a subgroup of \(G,\) and let \(\tau: H \rightarrow G^{\prime}\) be the restriction of \(\rho\) to \(H\). Show that \(\tau\) is a group homomorphism and that \(\operatorname{Ker} \tau=\operatorname{Ker} \rho \cap H\).
Let \(H\) be a subgroup of an abelian group \(G,\) and let \(a, b \in G\) with \(a \equiv b(\bmod H) .\) Show that \(k a \equiv k b(\bmod H)\) for all \(k \in \mathbb{Z}\).
Let \(\rho_{i}: G_{i} \rightarrow G_{i}^{\prime},\) for \(i=1, \ldots, k,\) be group homomorphisms. Show that the map $$ \begin{aligned} \rho: \quad G_{1} \times \cdots \times G_{k} & \rightarrow G_{1}^{\prime} \times \cdots \times G_{k}^{\prime} \\ \left(a_{1}, \ldots, a_{k}\right) & \mapsto\left(\rho_{1}\left(a_{1}\right), \ldots, \rho_{k}\left(a_{k}\right)\right) \end{aligned} $$ is a group homomorphism. Also show that if each \(\rho_{i}\) is an isomorphism, then so is \(\rho .\)
Let \(n\) be a positive integer, and let \(m\) be any integer. Show that \(\left[\mathbb{Z}_{n}: m \mathbb{Z}_{n}\right]=n / \operatorname{gcd}(m, n)\)
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