# CCSS IP Math I 2.1.3 Example 3

Use the vertical line test to determine if each relation is a function.

- Pass a vertical line over the figure in Graph A. Notice that the line crosses two points on the figure at the same time. The relation is not a function.
- Pass a vertical line over the curve in Graph B. Notice that at any time the vertical line only crosses 1 point on the curve at a time. The relation is a function.