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(1) Prove that for any finitely generated abelian group G, the set Hom(G, Z) is a free Abelian group of finite rank.

(2) Find the rank of Hom(G,Z) if the group G is generated by three generators x, y, z with relations 2x + 3y + z = 0, 2y - z = 0

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(i) Apply the structure theorem: write $G \simeq \mathbb{Z}^r \oplus_i \mathbb{Z}/d_i$ Now from here we compute $Hom(\mathbb{Z}^r \oplus_i \mathbb{Z}/d_i, \mathbb{Z}) \simeq Hom(\mathbb{Z}^r, \mathbb{Z}) \oplus_i Hom(\mathbb{Z}/d_i, \mathbb{Z}) \simeq \mathbb{Z}^r$

(ii) We just need to find the rank of the free part of $G$, we have it cut out as the cokernel of the map $\mathbb{Z}^2 \rightarrow \mathbb{Z}^3$, given by $\begin{pmatrix} 2 & 0 \\ 3 & 2 \\ 1 & -1 \end{pmatrix} \sim \begin{pmatrix} 2 & 2 \\ 3 & 5 \\ 1 & 0 \end{pmatrix} \sim \begin{pmatrix} 0 & 2 \\ 0 & 5 \\ 1 & 0 \end{pmatrix} \sim \begin{pmatrix} 0 & 0\\ 0 & 1 \\ 1 & 0 \end{pmatrix}$

So if I didn't goof that up, our group is simply $\mathbb{Z}^3/\mathbb{Z}^2 \simeq \mathbb{Z}$, and hence Hom is again $\mathbb{Z}$.

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    I'd think that if you're being asked to prove this (for homework? exam prep?) you probably were showed it in class? It's proved in probably any algebra textbook. The rank of $\mathbb{Z}$ as a $\mathbb{Z}$ module is 1.2012-12-13