Q. 1 C

Determine whether each of the following operations define a binary operation on the given set or not:

‘*’ on N defined by a * b = a + b – 2 for all a,b N.

Answer :

Given that ‘*’ is an operation that is valid in the Natural Numbers ‘N’ and it is defined as given:


a*b = a + b – 2, where a,bN


Since aN and bN,


According to the problem it is given that on applying the operation ‘*’ for two given natural numbers it gives a natural number as a result of the operation,


a*bN ...... (1)


Let us take the values of a = 1 and b = 1, substituting in the R.H.S side we get,


a + b – 2 = 1 + 1 – 2


a + b – 2 = 0N ...... (2)


From (2), we can see that a + b – 2 doesn’t give only Natural numbers as a result. So, this cannot be stated as a binary function.


The operation ‘*’ does not define a binary operation on N.


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