If a and b belong to Z[√d], where d is not divisible by the square ofa prime and ab is a unit, prove that a and b are units.

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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If a and b belong to Z[√d], where d is not divisible by the square of
a prime and ab is a unit, prove that a and b are units.

Expert Solution
Step 1

Let d be an integer that is not divisible by the square of a prime.

Let a and b belong to Zd and ab is a unit.

Here we need to that a and b are units.

Now, claim the statement,

"The only units of Zd are +1 and -1".

It is given that Na+bd=a2-bd2.

Let x=a+bdZd be a unit in Zd.

Note that x is a unit in Zd if and only if Nx=1.

So,

Nx=Na+bd=a2-db2=1

 

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