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jr16
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Homework Statement
Consider the subset H = {0,3} of the group Z6.
(i) Prove that H is a normal subgroup of Z6.
(ii) Prove that Z6/H is isomorphic to Z3. (Give an explicit isomorphism)
Homework Equations
In order to be a subgroup H must be closed under +6, have an identity, and have an inverse for each element.
In order to be a normal subgroup, the left cosets must equal the right cosets of H in Z6.
The Attempt at a Solution
(i) H is closed under +6
I wrote out the group table:
0 +6 0 = 0
3 +6 0 = 3
0 +6 3 = 3
3 +6 3 = 0
Therefore, H is closed.
the identity, e, is also in H
e = 0
0 +6 0 = 0
3 +6 0 = 3
Therefore, e is in H.
the inverse of a, a-1, is in H
0 +6 0 = 0
3 +6 3 = 0
Thus, a = a-1
Therefore, a-1 is in H.
Since all three conditions hold, H must be a subgroup of Z6.
Is H a normal subgroup of Z6?
left cosets:
aH =
0 +6 H = {0,3}
1 +6 H = {1,4}
2 +6 H = {2,5)
right cosets:
Ha =
H +6 0 = {0,3}
H +6 1 = {1,4}
H +6 2 = {2,5}
The left cosets = the right cosets of H in Z6.
Thus, H is a normal subgroup of Z6.
Is the above work correct?
Part (ii) I do not know where to even begin.
What does Z6/H mean? Is it possible to draw a group table for it?
I would really appreciate some heavy guidance on this portion.
Thank you so much for any help you can provide me!