Functions and one-to-one tests

Vertical line testing A relation is a function on the specified domain if every vertical line cuts its graph at at most one point. To show it is not a function, give a specific vertical line x=k that cuts the graph twice or more. Function: each vertical line cuts at most once. Function: each vertical line cuts at most once. Non-function: the displayed vertical line cuts more than once. Non-function: the displayed vertical line cuts more than once. Horizontal line testing A function is one-one if every horizontal line cuts its graph at at most one point. To show it is not one-one, give a specific horizontal line y=k that cuts the graph twice or more. One-one function One-one function Not one-one Not one-one