To know from a graph if it is a function or not we just need to look if the relation between the x-values and the y-values.
To be a function for each x-value there is just one y-value. If for a x-value there is two or more values of y, it is not a function. So let's look at our graphs:
As we can see above for the first three graphs, all are not functions once there are a least on or more x-values with more than one corresponding y-value. Let's look over the next three graphs:
As we can see above, graph 4, 5 and 6 represent a function once for all x-values, there are only one y-value.
NOTE: - For graph 5 We can see there are empty circles what means it is an open interval, so that points does not count.
- The x-values I mentioned are only the x-values for the functions.
