Functions

Functions can also be written in the form of an equation.

Suppose that your monthly mobile phone bill is a function of the length of your call usage in minutes and that such function is denoted by the equation $y=6.5x.$

The variable x represents the length of your call usage in minutes and the variable y represents your monthly phone bill. Moreover, the constant 6.5 is the rate or charge per minute of your call. Observe that for every value of x, there is exactly one value of y.

In the equation $y=6.5x,$ the variable x can be assigned with any value that is greater than or equal to zero since it represents an amount of time in minutes. The variable x is called the independent variable, while the variable y is called the dependent variable.