Is this a function or what?

Question

Answer 1

I can't access the image, but I can give a general rule:

The graph of a mathematical formula relating x (the independent variable) to y (the dependent variable) can only be a function if there is only one possible value of y for each value of x.

Any vertical line drawn cannot intersect the graph of a function more than once. For example:

is a function but is not a function.