6
1. FUNCTIONS AND LINEAR MODELS
Vertical Line Test. If every vertical line drawn on a graph intersects the
graph in at most one point, then the graph is the graph of a function. Otherwise
the graph is not the graph of a function.
function
not a function
Some functions are discontinuous, i.e., they have a break in them.
(
)
x,
x<0
Example. g(x) =
is a function.
x + 1, x 0
The open dot at (0, 0) indicates that (0, 0) is not a point of the graph, while
the closed dot indicates (0, 1) is part of the graph.