Exercise 1 Page 275

For a relation to be a function, each x-value can only be paired with one y-value, but one y-value can be paired with multiple x-values. In a graph, we can check if each x-value has only one y-value by subjecting it to the Vertical Line Test.

On the given graph, there is no visible part where two points have the same y-value. Each vertical line passes through the graph at only one point, so the graph is a function.