2-1 Relations and Functions The Domain of a relation is all the input numbers. The Range of a relation is the output numbers. A relation is a set of pairs of input and out put values. Relations can be wrote as a set of ordered pairs. input Graphing a relation domain Relation- (8,11),(4,9) (8,11) (6,7) (4,9) output range A function is a relation when each element of the domain is paired with exactly one element of the range. Another way to show a relation is to use a mapping diagram. This links each domain with the corresponding range. domain range

Not a function This is a function 5 1 2 3 4 5 1 6 6 2 This is not a function because the red line hits the blue line in three different places. 7 8 3 7 This is a function The vertical-line test is to see whether a line passes through more then one point at a time. If it does pass over two or more points at a time then the relation is not a function.