Variables can be broken down into independent and dependent variables. An independent variable is a quantity that increases or decreases (is variable), or that has an infinite number of values in the same expression. For example, in the expression x2 + y2 = r2, x and y are variables. A dependent variable is a quantity that varies, but is produced by changes in the independent variable. In other words, the dependent variable’s value is dependent on the independent variable. For example, in the expression f(x) = y, x is the independent variable and y is a dependent variable (because y is dependent on the value of x).