15. If φ: Sn Sn is a group homomorphism, prove that φ(An) c An. (Hint: Use Lemma 4.7.) a 4.7. Let n 2 3. Every element...
Let A be a subset of a finite group G with |A| > |G|/2. Prove that every element of G can be written as the product of two elements of A. Is this also always true when |A| = |G|/2?
9) A group G is called solvable if there is a sequence of subgroups such that each quotient Gi/Gi-1 is abelian. Here Gi-1 Gi means Gi-1 is a normal subgroup of Gi. For example, any abelian group is solvable: If G s abelian, take Go f1), Gi- G. Then G1/Go G is abelian and hence G is solvable (a) Show that S3 is solvable Suggestion: Let Go- [l),Gı-(123)), and G2 -G. Here (123)) is the subgroup generated by the 3-cycle...
OTO (7) (a) Let T = (a1, ..., ak) be a k-cycle in Sn, and let o E Sn. Prove that is the k-cycle (o(a), o(az),..., 0(ak)) (b) Let o,t e Sn. Prove that if t is a product of r pairwise disjoint cycles of lengths k1,..., kr, respectively, where kit..., +kr = n, then oto-1 is also a product of r pairwise disjoint cycles of lengths k1,..., kr. (c) Let T1 and T2 be permutations in Sn. Prove that...
6. Let si = 4 and sn +1 (sn +-) for n > 0. Prove lim n→oo sn exists and find limn-oo Sn. (Hint: First use induction to show sn 2 2 and the.show (sn) is decreasing)
2. Let p: G -G be a surjective group homomorphism (a) Show that if G is abelian then G' is abelian. (b) Show that if G' is cyclic then there is a surjective homomorphism from (Z, +, 0) to G'. (Hint: use the fact that Z is generated by 1 and G' has a generator). (c) Use Part (a) and (b) to show that every cyclic group is abelian.
3 (Due 8/7) Prove that every element of a group has a unique inverse. (Due 8/7) Let (G, *) be a group and let a be an element of G with inverse d'. Prove that the function f(x) = a*r*d' is a permutation of G.
(4) Let p Z be a prime. Prove that zli/(p+1) has exactly ] p2 +1 elements. Use that 5+5i (2+i)(3+i) to determine how many elements Zu/5+5i) has. (5) Let m,n be integers with m|n. Prove that the surjective ring homomor- phism Z/n -> Z/m induces a group homomorphism on units, and that this group homomorphism is also surjective. (4) Let p Z be a prime. Prove that zli/(p+1) has exactly ] p2 +1 elements. Use that 5+5i (2+i)(3+i) to determine...
10. Let G = D. be the dihedral group on the octagon and let N = (r) be the subgroup of G generated by r4. (a) Prove that N is a normal subgroup of G. (b) If G =D3/N, find G. (c) Using the bar notation for cosets, show that G = {e, F, 2, 3, 5, 87, 82, 83}. Hint: Show that the RHS consists of distinct elements and then use part (b). (d) Prove that G-D4. Hint: It...
Please help answer all parts! (1) Prove that 75 is irrational. (State the Lemma that you will need in the proof. You do not need to prove the lemma.) (2) Disprove: The product of any rational number and any irrational number is irrational. (3) Fix the following statement so that it is true and prove it: The product of any rational number and any irrational number is irrational. (4) Prove that there is not a smallest real number greater than...