The Vertical Line Test
You can check whether a graph represents a function by using the vertical line test.
The test states that a graph represents a function if and only if all vertical lines intersect the graph at most once.
Example:
This graph does not represent a function: for example, the vertical line x = 1 intersects it in three places. |
This graph does represent a function, since any vertical line intersects the graph exactly once, except x = 0, which doesn't intersect it at all. |
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