1. If A and B are normal subgroups of G such that G/A and G/B are abelian, prove that G/(A intersect B) is abelian
2. Let H and K be groups, let f be a homomorphism from K into Aut(H) and as usual identify H and K as subgroups of G= H x_f K( x_f denotes product of H and K under f).
Prove that C_K(H)= Ker(f)
ps. C_K(H) is centralizer
keywords: semi direct