What is the reverse process of differentiation used for?

The reverse process of differentiation is known as integration, and it is primarily used for calculating the area under curves. When you integrate a function, you find the accumulated value or total area that the function occupies over a specified interval. This is particularly important in various fields such as physics and engineering, where determining the area under a curve can correspond to quantities like distance, work done, or total population over time.

In contrast, the other options involve different mathematical processes. Calculating limits is related to the behavior of functions as they approach certain points; finding gradients pertain directly to differentiation itself; and graphing functions is a separate activity that may involve both differentiation and integration but does not inherently require the reverse process. Thus, the correct association of integration is with calculating the area under curves, making it the most appropriate choice.