The set of all inputs of a relation or function.
A relation in which each input has only one output. Often denoted f (x).
Horizontal Line Test
If every horizontal line you can draw passes through only 1 point, x is a function of y. If you can draw a horizontal line that passes through 2 points, x is not a function of y.
The set of all outputs of a relation or function.
A set of inputs and outputs, often written as ordered pairs (input, output).
The domain of a function that is not defined for all real numbers.
Vertical Line Test
If every vertical line you can draw goes through only 1 point, y is a function of x. If you can draw a vertical line that goes through 2 points, y is not a function of x.