Mathematics Asked by user723228 on February 23, 2021
Show that $mathbb{Z}/5mathbb{Z} = langle arangle$.
I have that $a$ is an element of the non zero complex numbers $mathbb{C}^*$ and $a^{5}=1$ where $a neq 1$. I have shown already that $|a| = 5$ and the function that maps $(mathbb{Z},+) to (mathbb{C}^*,times)$ given by $n mapsto a^n$ is a homomorphism.
How do I now go on to show that $mathbb{Z}/5mathbb{Z} = langle arangle$?
Actually $mathbb{Z}/5mathbb{Z}$ is a cyclic group of order $5$, and since $5$ is prime then all the non-identity elements of $mathbb{Z}/5mathbb{Z}$ are of order $5$ then all the non-identity elements are generators of this group. Now, $a$ is an element of $mathbb{C}^*$ and a is not identity and $a^5=1$ then $|a|=5$ and $<a>$ is a cyclic group of order $5$ and having the elements ${a,a^2,a^3,a^4,1}$ where all the elements are of order $5$. So, ${a,a^2,a^3,a^4,1}$ is isomorphic to $mathbb{Z}/5mathbb{Z}$, Hence , $mathbb{Z}/5mathbb{Z}=<a>$. Is my way correct or convincing?
Answered by RIT on February 23, 2021
Denote your homomorphism by $varphi$. Using the fact that the order of $a$ is $5$, one can show that Ker $varphi$ = $5mathbb{Z}$. Now, the fundamental homomorphism theorem for groups says that $mathbb{Z}/$Ker $varphi$ $cong$ Im $varphi$. Now we have Im $varphi = ⟨a⟩$ such that $mathbb{Z}$/ $5mathbb{Z} cong ⟨a⟩$.
Answered by CrackedBauxite on February 23, 2021
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