For example, the size relationship between f(x) and g(x) on question (a, b).

At this time, the function h(x)=f(x)-g(x) can be constructed, and then the positive and negative of h(x) on (a, b) can be calculated, so that the size relationship between f(x) and g(x) can be known.

Of course, sometimes it is easy to know the relationship between g(x) and another function m(x), such as ln (x+ 1) ≤ x (x >- 1). At this time, n(x)=f(x)-m(x) can be constructed.