If it is a high school level, we can use the infinitesimal method, that is, divide the graphic area into n rectangles with equal distance, calculate their sum, and then calculate the limit of the sum of areas when n approaches infinity. This method is often used in high school physics, mathematics and textbooks. But after all, it is only for some very special curves, such as parabola. The curves of other general equations cannot be found;

If it is a university level, it is best to use integral, but it also has certain limitations. A considerable part of it is difficult to accumulate, and it is necessary to look up tables or even computers. ...