a) List all the cyclic subgroups of <Z10, +> (Z10 = integers mod 10)
b) Show that Z10 is generated by 2 and 5
c) Show that Z2 x Z3 is a cyclic group
Any help is appreciated.... Thanks.
Take every element and work out the subgroup generated by them. For example, $\displaystyle <5> = \{5, 0\}$ as $\displaystyle 5+5=0$.
$\displaystyle Z_{10} = <1>$. That is to say, it is generated by the element 1. So, if you can prove that $\displaystyle 1 \in <2, 5>$ then you are done. You can prove that $\displaystyle 1 \in <2, 5>$ by noting that 2 and 5 are coprime, so...
You want to find a single element which generates this group. So, try a few...