Let G be a group. Consider the set G with a new operation ∗
given by...
Let G be a group. Consider the set G with a new operation ∗
given by a ∗ b = ba. Show that (G, ∗) is a group isomorphic to the
original group G. Give an explicit isomorphism.
Let G be a group acting on a set S, and let H be a group acting
on a set T. The product group G × H acts on the disjoint union S ∪
T as follows. For all g ∈ G, h ∈ H,
s ∈ S and t ∈ T,
(g, h) · s = g · s, (g, h) · t = h · t.
(a) Consider the groups G = C4, H = C5,
each acting...
Let G be a group with the binary operation of juxtaposition and
identity e. Let H be a subgroup of G.
(a) (4 points) Prove that a binary relation on G defined by a ∼
b if and only if a−1b ∈ H, is an equivalence.
(b) (3 points) For all a ∈ G, denote by [a] the equivalence
class of a with respect to ∼ . Prove that [a] = {ah|h ∈ H}. We
write [a] = aH and...
Let G be a group. The center of
G is the set
Z(G) = {g∈G
|gh = hg
∀h∈G}. For
a∈G, the centralizer of
a is the set
C(a)
={g∈G |ga
=ag }
(a)Prove that Z(G) is an
abelian subgroup of G.
(b)Compute the center of D4.
(c)Compute the center of the group G of the shuffles of three
objects x1,x2,x3.
○n: no shuffling occurred
○s12: swap the first and second items
○s13: swap the first and third items
○s23:...
Let (G,·) be a finite group, and let S be a set with the same
cardinality as G. Then there is a bijection μ:S→G . We can give a
group structure to S by defining a binary operation *on S, as
follows. For x,y∈ S, define x*y=z where z∈S such that μ(z) =
g_{1}·g_{2}, where μ(x)=g_{1} and μ(y)=g_{2}.
First prove that (S,*) is a group.
Then, what can you say about the bijection μ?
Let G be a group and a be an element of G. Let φ:Z→G be a map
defined by φ(n) =a^{n} for all n∈Z. a)Show that φ is a group
homomorphism. b) Find the image ofφ, i.e.φ(Z), and prove that it is
a subgroup ofG.
Let
G be a finite group and H a subgroup of G. Let a be an element of G
and aH = {ah : h is an element of H} be a left coset of H. If b is
an element of G as well and the intersection of aH bH is non-empty
then aH and bH contain the same number of elements in G. Thus
conclude that the number of elements in H, o(H), divides the number
of elements...
Let G be a group, and let a ∈ G be a fixed element. Define a
function Φ : G → G by Φ(x) = ax−1a−1.
Prove that Φ is an isomorphism is and only if the group G is
abelian.
Let G be a group and K ⊂ G be a normal subgroup. Let H ⊂ G be a
subgroup of G such that K ⊂ H Suppose that H is also a normal
subgroup of G. (a) Show that H/K ⊂ G/K is a normal subgroup. (b)
Show that G/H is isomorphic to (G/K)/(H/K).
Let A and B be groups, and consider the product group G=A x
B.
(a) Prove that N={(ea,b) E A x B| b E B} is a
subgroup.
(b) Prove that N is isomorphic to B
(c) Prove that N is a normal subgroup of G
(d) Prove that G|N is isomorphic to A