Precalculus (6th Edition)

The given graph represents a function. domain: $(-\infty, +\infty)$ range: $(-\infty, 4]$
Note that all vertical lines will pass through the graph in at most one point. This means that the graph pass the vertical line test. Thus, the given graph represents a function. The graph covers all real numbers from left to right so the function is defined for all values of $x$. This means the domain is $(-\infty, +\infty)$. The y-values are from $4$ and below. This means the range is $(-\infty, 4]$.