subgroups
Let H and K be subgroups of an abelian group G and let HK := {ab : a ? H and b ? K}.(a) Prove that HK is a subgroup of G.(b) Give an example to show that part (a) may be false if G is not abelian.
WE ACCEPT
Let H and K be subgroups of an abelian group G and let HK := {ab : a ? H and b ? K}.(a) Prove that HK is a subgroup of G.(b) Give an example to show that part (a) may be false if G is not abelian.