1.

Let S be the set of all points in a plane and R be a relation on S defines as `R={(P,Q):` distance between `P and Q` is less than 2 units} Show that R is reflexive and symmetric but not transitive.

Answer» `R = {(P,Q):` distance between `P` and `Q` is less than `2` units.
`R` is reflexive as point `P` will have `0` unit distance with `P` which is less than `2`.
So, `(P,P) in R`.
Now,
Let `(P,Q) in R`.
`=>` Distance between `P` and `Q` is less than `2` units.
`=>` Distance between `Q` and `P` is less than `2` units.
`:. (Q,P) in R`.
`:. R` is symmetric.
Now,
Let `(P,Q) in R and (Q, S) in R`
It means distance between `P` and `Q` is less than `2` units and distance between `Q` and `S` is less than `2` units.
But it is not neccessary, distance beteen `P` and `S` is less than `2` units.
`=> (P,S) notinR`.
`:. R` is not transitive.
Therefore, `R` is reflexive and symmetric but not transitive.


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