has larger values for x large.
From the two graphs above, it appears that y = x7 is the answer. However, if we make x larger then we see the following graph which leads us to a different conclusion. This, in fact, can be verified by using l'Hospital's Rule.
Two alternative methods for doing this type of investigations are to consider the graph of y = x7 - 4x:
or the graph of y = x7 / 4x: