If $H$ and $K$ are solvable subgroups of G with $H$ normal in $G$, then $HK$ is a solvable subgroup of $G$.
I know a group is solvable if and only if it has a solvable series. But I don't know how to construct the solvable series of $HK$.
If $H$ and $K$ are solvable subgroups of G with $H$ normal in $G$, then $HK$ is a solvable subgroup of $G$.
I know a group is solvable if and only if it has a solvable series. But I don't know how to construct the solvable series of $HK$.