Let G be a group and suppose H = {g5 : g ∈ G} is a subgroup of G.
(a) Prove that H is normal subgroup of G.
(b) Prove that every element in G/H has order at most 5.
a) Consider
And is arbitrary
Then we have
This is because as the terms cancel out (the outer a inverse and inner a)
So that also
Meaning must be a normal subgroup
b) Let
Then we have so that is the identity element
This means the order of an element must be less than or equal to 5
That is, every element can have order at most 5
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