a. Function
b. Function
c. Not a function
d. Function
It’s easy to tell if a graph or a data table is a function or not. For a graph, use the vertical line test. Simple draw or imagine a vertical line straight down from the top to the bottom of the graph. The vertical line can only touch the line on the graph once, anything more than once will fail it as a function. So like circles will fail the vertical line test, and therefore, is not a function. You also have to go through the whole graph, left to right, with the vertical line test.
For data tables, look out for x values. In one table, the same x value cannot happen more than once. If you see two same x values, it is not a function, if not, it is. So as you see in the third one, there are duplicates of -100, -25, and -4. Whereas in others, there are no duplicate x values.