MATHS302 Assignment 3
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MATHS302 Assignment 3
1. Without using the odd order theorem or the pa qb theorem (which we have not proved) show that groups of these orders are not simple.
(a) |G| = 45
(b) |G| = 55
(c) |G| = 70
(d) |G| = 75
(e) |G| = 196
2. An automorphism of a group G is an isomorphism π : G -→ G from G to itself. Prove that the set of all automorphisms of a finite group G with the operation of function composition forms a finite group denoted Aut(G), the automorphism group of G.
3. Describe Aut(Zp ), the automorphism group of the cyclic group Zp where p is
prime. In particular find the order of this group.
(Hint: A generator must map to another generator)
4. A subgroup is called characteristic if it is invariant under all automorphisms. We write H char G if θ(h) e H for all h e H and θ e Aut(G). We may think of this as being a stronger type of normality. Prove that a characteristic subgroup is normal and give a counterexample to show that a normal subgroup need not be characteristic.
Hint: In an abelian group all subgroups are normal. Are they call characteris- tic?
5. If K char H 4 G prove that K 4 G.
6. Show that if a Sylow P subgroup is normal then it is characteristic.
7. If M is a proper subgroup of G we call it maximal if M < X < G implies X = M or X = G. The Frattini subgroup of a group G is defined to be the intersection of all the maximal subgroups.
(a) Prove that the Frattini subgroup Fratt(G) is characteristic in G.
(b) If H < G and H.Fratt(G) = G show that H = G. (Hint: If H < G then there is a maximal subgroup M with H < M)
8. If N 4 G and both G and G/N are soluble, show that G is soluble.
9. Give a counterexample to show that this is not true if yuo replace the word ”soluble” with ”nilpotent. That is show that if G and G/N are both nilpotent then it need not be the case that G is nilpotent.
10. Prove that [G, N] < N 兮 N 4 G.
2022-06-06