Let H, K be subgroups of G. Prove:
H \cap K is also a subgroup. Is H \cup K a subgroup?
Let H, K be subgroups of G. Prove:H K is also a subgroup. Is H K a subgroup?
Let H, K be subgroups of G. Prove:
H \cap K is also a subgroup. Is H \cup K a subgroup?