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    				| 1. | 
                                    Let a* b =1cm (a,b) for all values of a,b in N (i) Find (12*16) (ii) Show that* is commutative on N (iii) Find the identity element in N (iv) Find all invertible elements in N | 
                            
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Answer»  (ii)a*B=1cm (a,b) =1cm (b,a)=b*a (iii) let e be the identity element in N (iv) Let a in N be an ARBITRARY element Then `a*b=1 rarr 1cm (a,b)=1 rarr a=b=1` `therefore` 1 is the only element in N which is ivertible  
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