I need your help in proving these two statements:
1) Let G be a finite group and let H and K be two subgroups of G such that [G:H]=p and [G:k]=q, where p and q are disinct primes. Prove that pq divides [G:H(intersection)k]
We have that , so , so...
2) Let G be a group all of whose subgroups are normal. If a,b are in G, prove that there is an integer k such that ab=b(a^k)
Take the subgroup , then for any (why?), so...