Algebra: Chapter 12, Lesson 1 and Lesson 2, page 536 and 542.
Relations and Functions and Graphs
A relation is a set or ordered pairs. The domain of a relation is the set of first coordinates (the x’s). The range is the set of second (or y) coordinates.
A function is a relation that assigns one member of the domain EXACTLY one member of the range. In other words, one x can have ONLY one y value.
You can evaluate a function `f(x)=2x^2 + 5` for `f(2)` by substituting 2 for every x that you see. In our example then, `f(2)=2⋅4 + 5 = 13`
You can recognize a function with the vertical line test. You can find the domain and range of a function by seeing where the function is not defined. Good examples are `−`, we can’t take square roots of negative numbers and we cannot have `1/0` because that results in infinity or an undefined solution.
Here again, is a great link for Purplemath.