Q.

Let the relations R1 and R2 on the set X={1,2,3,...,20} be given by R1={(x,y):2x-3y=2} and R2={(x,y):-5x+4y=0}. If M and N be the minimum number of elements required to be added in R1 and R2, respectively, in order to make the relations symmetric, then M+N equals                  [2024]

1 10  
2 8  
3 16  
4 12  

Ans.

(1)

    R1={(x,y):2x-3y=2}

    R1={(4,2),(7,4),(10,6),(13,8),(16,10),(19,12)}

   So, 6 elements are needed to make R1 symmetric

   M=6

   R2={(x,y):-5x+4y=0}

   R2={(4,5),(8,10),(12,15),(16,20)}

   So, 4 elements are needed to make R2 symmetric

  N=4

  M+N=6+4=10