Definition of definite integral

Definition of definite integral

The definite integral is derived from the area problem of plane figure. As shown in the figure on the right, y = f (x) is a function defined on [a, b]. In order to find the area s of the figure surrounded by x = a, x = B, y = 0 and Y = f (x), the ancient Greek's exhaustion method is adopted. First, the approximate value of S is obtained by replacing the curve with the straight in a small range, and then the area s is obtained by taking the limit