expressed A∪B

e.g.

A = {1,2,3,4}

B = {2,4,6}

so, A∪B = {1,2,3,4,6} Sets of ordered pairs

· the order within each pair matters

· a relation is only a function if each element of the domain occurs only once as a first component

e.g.

R = {(a,b),(a,c),(b,c),(c,d)}

Domain = {a,b,c}

Range = {b,c,d}

*NOT a function because the domain "a" occurs twice relation with all the ordered pairs reversed

e.g.

inverse of R = {(1,2),(3,4),(5,6)} = {(2,1),(4,3),(6,5)} 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196, 225 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47