Domain and range

The range is the set of all possible outputs (” $y$ “-values) of a function.

We denote the range of a function $f$ by $R_f$ .

Graphs are especially useful to determine the range of a function.
End points, turning points and asymptotes are important in determining the range.

Examples

Use the following to generate functions and observe how their range can be determined from the graph.

{f: x \mapsto - x^2 + 4 x - 9} \allowbreak \quad \allowbreak {\textrm{for } x \in \mathbb{R}, x \leq 2.}

\begin{aligned} D_f &= \left(-\infty, 2\right]. \\ R_f &= \left(-\infty, -5 \right]. \end{aligned}