1.

Show that * on Z+ defined by a *b = |a –b| is not a binary operation.

Answer»

To prove: * is not a binary operation 

Given: a and b are defined on positive integer set 

And a*b = |a - b| 

⇒ a*b = (a - b), when a>b 

= b - a when b>a 

= 0 when a = b 

But 0 is neither positive nor negative. 

So 0 does not belong to Z+

So a*b = |a - b| does not belong to Z+ for all values of a and b 

So * is not a binary operation.

Hence proved



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