For any subgroup H of G and any non-empty subset A of G define NH(A)={h∈H|hAh−1=A} . Show that NH(A)=NG(A)∩H and dedue that NH(A)≤H .
Adv.
Let h≤G . Let N=⋂x∈GxHx−1 . Prove that N≤G, and aNa−1=N for all a∈G .
If H is a subgroup of finite index in G , prove that there is only a finite number of distinct subgroups in G of the form aHa−1 .
If H is of finite index in G, prove that there is a subgroup N of G, contained in H and of finite index in G such that aNa−1=N for all a∈G .
Let G be a finite group. Show that the only homomorphism from G to (Z,+)( or to (Q,+) or to (R,+)) is the zero homomorphism.
Show that any endomorphism of (Q,+) is multiplication by a rational number.
Prove that there is no non-trivial homomorphism from
(i) (Q,+) to (Z,+)
(ii) (Q,+) to (Zm,+)
(iii) (Q,+)to (Q∗,×), where Q∗=Q−{0}.
Prove that there is no surjective homomorphism from
(i) Z16×Z2 to Z4×Z4 (ii) Z4×Z4 to Z8 .
If ϕ is a homomorphism from Z30 onto a group of order 5, determine ker ϕ .
Let G be an abelian group and n a positive integer. Define f:G→G by f(x)=xn . Show that f is an endomorphism of G. Further if G is finite such that n and |G| are coprime, show that f is an automorphism of G .
If a group G contains an element a with exactly two conjugates, then show that G has a normal subgroup N≠{e} .
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