Let a and ß belong to S,. Prove that aß is even if and only if a and B are both even or both odd.

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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Let a and ß belong to S,. Prove that aß is even if and only if a
and B are both even or both odd.
Transcribed Image Text:Let a and ß belong to S,. Prove that aß is even if and only if a and B are both even or both odd.
Expert Solution
Step 1

Given: Let α , β belong to Sn.

Prove that: αβ is even if and only if α , β both are even or odd.

 

Step 2

Let α , β belong to Sn.

Theorem: If a permutation f is expressed as a product of transposition then the number of transpositions is either always even or odd.

Let αβ is even permutation.

αβ is expressed as the product of an even number of transpositions.....[1]

If α is a product of r number of transpositions and β is product of m number of transpositions which implies that αβis a product of a number r+m of transpositions............[2]

Now using statements [1] and [2]

r+m is even.

Which is only possible if both r , m are even or both are odd.

Therefore,α , β both are even or odd.

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