1.

Show that the union of two equivalence relations on a set is not necessarily an equivalence relation on the set.

Answer» Let `R_(1) and R_(2) ` be two relations on a set `A={1,2,3}.` given by
`R_(1)={(1,1),(2,2),(3,3),(1,2),(2,1)}.`
`and R_(2) ={(1,1),(2,2),(3,3),(1,3),(1,3),(3,1)}.`
then it is easy to verify that each one of `R_(1) and R_(2)` is an equivalence relation .
But ,`R_(1) cup R_(2) ={(1,1),(2,2),(3,3),(1,2),(2,1) ,(1,3) ,(3,1)}.`
is not transitive ,as
`(3,1)in R_(1) cup R_(2) and (1,2) in R_(1) cup R_(2) but (3,2) !in R_(1) cup R_(2).`
hence `(R_(1) cupR_(2) )` is not an equivalence relation .


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