# The Definite Integral

In this section we continue to compute areas using rectangles. Doing this allows us to undo the process of taking the derivative of a function. From the derivative of a function, we can estimate changes in the function and make the estimates arbitrarily close.

By using more and more rectangles over an interval, the area of the rectangles approach the area between the derivative function and the x axis over the interval. This area is the exact change in the original function and is represented by a definite integral.