IXL Algebra1 - Q.5 Identify Functions: The Vertical Line Test

The vertical line test allows us to visualize what happens when a single value for x gives multiple outcomes and identifies the graph of a relation as non-functional. A vertical line represents all the points with the same x value ... like x =2 is a vertical line with points like (2,0), (2,-2), (2,9), (2, 12) and so on.

If you ever get a value for x that yields more than one output value, then the relation is NOT a function.