The domain, $D,$ is the set of all $x$-values or inputs for which a function is defined. There are two reasons for numbers to be excluded from the domain:

• The number gives a forbidden calculation, such as $\sqrt{\text{-}1}$ or $\frac{2}{0}.$
• The function describes a specific situation. Suppose, for example, $f(x)$ represents the price of $x$ apples. It does not make sense to consider the cost of $\text{-} 5$ apples. Thus, $\text{-} 5$ would not be in the domain of $f(x).$

Since $y$ is a function of $x,$ the range depends on the domain .