How can you tell if a table graph or chart represents a function

A function is a function if each x only has one y.

In a graph you can see this by doing a vertical line test. This would just be taking a vertical line and sliding it across the graph: if there is more than 1 point at any of the sections of the graph, then it's not a function.

In a table and chart: looking at the x's and if the same x value appears twice it's not a function.