Domain of a function is which of the following?

• A. All the Y values in a function
• B. All the X values in a function
• C. The maximum value of the function
• D. The set of ordered pairs that make up the function

Answer: (B)

The domain is about the inputs. The domain of a function is the set of all input values x for which f(x) is defined. It tells you which x-values you can plug into the rule without hitting undefined or impossible things (like dividing by zero or taking a square root of a negative number). So the domain corresponds to the set of X values in the function.

For contrast, the Y values you get as outputs form the range, the maximum value is only defined if the function actually has a largest output, and the set of all ordered pairs describes the whole relation, not just the inputs. That’s why the correct description is the set of all input values.