Q.13 Show that the relation R defined in the set A of all polygons as , is an equivalence relation. What is the set of all elements in A related to the right angle triangle T with sides 3, 4 and 5?
Same polygon has same number of sides with itself,i.e. , so it is reflexive.
Let,
i.e.P1 have same number of sides as P2
P1 have same number of sides as P2 is same as P2 have same number of sides as P1 i.e.
Hence,it is symmetric.
Let,
and i.e. P1 have same number of sides as P2 and P2 have same number of sides as P3
P1 have same number of sides as P3 i.e.
Hence, it is transitive,
Thus, , is an equivalence relation.
The elements in A related to the right angle triangle T with sides 3, 4 and 5 are those polygons which have 3 sides.
Hence, the set of all elements in A related to the right angle triangle T is set of all triangles.