Prove that every subgroup of Z is either the trivial group, {0}, or nZ = {nx | x E Z} for some n E N. %3D

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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Prove that every subgroup of Z is either the trivial group, {0}, or nZ = {nx | x E Z} for some n E N.
Transcribed Image Text:Prove that every subgroup of Z is either the trivial group, {0}, or nZ = {nx | x E Z} for some n E N.
Expert Solution
Step 1

To prove:

That every subgroup of  is either the trivial group{0} or n=nxxfor some n.

Proof:

Since,{0} is a trivial group of ,then there is nothing to prove.

Therefore,It is a subgroup of .

Now, we need to prove that n=nxxfor some n is the subgroup of .

a) First,It is closed under addition on n.

If a,bn, then there exist k1,k2,such that a=k1n  and b=k2n  .

Then,

a+b=k1n+k2n=k1+k2nn

b) The identity of , 0, is an element of n, since 0=n×0,so 0n.


(c) Finally, let’s show that any element of n has an inverse. Indeed if an, then a=k1n for some integer k1.

Then,

-a=-k1n=-k1nn.

Therefore ,the inverse of a is also an element of n.

Therefore, 

from(a),(b) and (c) 

n=nxxfor some n is a subgroup of .

 

 




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