In a function, one value of the input can be related to only one value of the output.
In a graph, it means that for each value of x(horizontal axis), there can only be one respective value of y(vertical axis), that is, there cannot be point that are aligned vertically.
In this problem:
On the first graph, there are points that are aligned vertically, for example, when x = -2, y = -2 and y = 2, hence, it is not a function.
On the 2nd and on the 3rd graph, there are no points aligned vertically, hence, they are functions.
To learn more about the function concept, you can take a look at https://brainly.com/question/12463448
