Let f be a continuous function on the closed interval [a, b], and f(x)≥0. The plane figure (Figure 9- 1) enclosed by curve y=f(x), straight line x=a, x=b and x axis is called a curved trapezoid. The area of the curved trapezoid is discussed below.

Practice: (1) Subparagraph. In the interval [a, b], randomly select n- 1 points, namely a = x0 < x 1 < x2.