Note the efficiency of this notation. In Example 1.1.1 the compact formula f(x) x2 4 completely defines the function, and you can indicate that 13 is the unique number the function assigns to 3 by simply writing f(3) 13.It is often convenient to represent a functional relationship by an equation y f(x), and in this context, x and y are called variables. In particular, since the numerical value of y is determined by that of x, we refer to y as the dependent vari- able and to x as the independent variable. There is nothing sacred about the sym- bols x and y. For example, the function y x2 4 can just as easily be represented by s t2 4 or by w u2 4. These formulas are equivalent because in each the independent variable is squared and the result is increased by 4 to produce the value for the dependent variable.Functional notation can also be used to describe tabular data. For instance, Table 1.1 lists the average tuition and fees for private 4-year colleges at 5-year intervals from 1973 to 2008.