Which statement describes the domain of a relation?

Which statement describes the domain of a relation?

• A. The set of x-values
• B. The set of y-values
• C. The ordered pairs
• D. The range

Answer: (A)

The domain is the set of all input values that appear in a relation. Since a relation is a collection of ordered pairs (x, y), the domain comes from the x-coordinates—the first elements of each pair. So, if you have pairs like (2, 3), (4, 1), (2, 5), the x-values are 2, 4, and 2 again, and the domain is the set {2, 4} (duplicates don’t appear in a set). The corresponding set of outputs, the y-values, is called the range, which would be {3, 1, 5} in that example. The ordered pairs themselves describe the relation as a whole, not just the inputs.

The domain is the set of all input values that appear in a relation. Since a relation is a collection of ordered pairs (x, y), the domain comes from the x-coordinates—the first elements of each pair. So, if you have pairs like (2, 3), (4, 1), (2, 5), the x-values are 2, 4, and 2 again, and the domain is the set {2, 4} (duplicates don’t appear in a set). The corresponding set of outputs, the y-values, is called the range, which would be {3, 1, 5} in that example. The ordered pairs themselves describe the relation as a whole, not just the inputs.