## Calculus 10th Edition

The graph with three roots is $f(x)$ and the other is $f'(x)$.
By checking the roots of one graph and the behavior of the other graph at those values, it can be decided which graph is which. The graph with three intersections has horizontal tangents where the other graph has roots, while nothing special happens to the graph with two intersections when the other graph has roots hence the graph with three roots is the $f(x)$ and the other is $f'(x).$