1.

Define * on N by m * n = 1 cm (m, n). Show that * is a binary operation which is commutative as well as associative.

Answer»

* is an operation as m*n = LCM (m, n) where m, n ∈ N. Let m = 2 and b = 3 two natural numbers. 

m*n = 2*3 

= LCM (2, 3) 

= 6∈ N 

So, * is a binary operation from N x N → N. 

For commutative, 

n*m = 3*2 

= LCM (3, 2) 

= 6∈ N 

Since m*n = n*m, hence * is commutative operation. 

Again, for associative, let p = 4 

m*(n*p) = 2*LCM (3, 4) 

= 2*12 

= LCM (2, 12) 

= 12∈ N 

(m*n) *p = LCM (2, 3) *4 

= 6*4 

= LCM (6, 4) 

= 12∈ N 

As m*(n*p) = (m*n) *p, hence * an associative operation.



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