3) In mathematics, a function is a relationship between two variables called the independent variable and the dependent variable. The dependent variable has at most one value for any specific value of the independent variable. A function is usually symbolized by a lowercase, italicized letter of the alphabet, followed by the independent variable in parentheses. For example, the expression y = f ( x ), read " y equals f of x ," means that a dependent variable y is a function of the independent variable x . Functions are often graphed, and they usually appear as lines or curves on a coordinate plane.