The figure shows a set of Cartesian axes labelled x and y concentrated in the upper-right and lower-right quadrants. A curve of y equals f of x is labelled. There are points a and b labelled on the positive x-axis with a being nearer the origin. The curve starts in the lower-right quadrant below the positive x-axis directly below the point a, it continues to a local maximum point in the upper-right quadrant and continues to the lower-right quadrant to finish at a point directly below the point b below the positive x-axis. The areas between the curve and the positive x-axis are shaded. The area between the point a and where the curve crosses from the lower-right to the upper-right quadrant is shaded below the positive x-axis and labelled with a minus sign, similarly so too is the area between where the curve crosses back from the upper-right to the lower-right quadrant to the point b. The area above the positive x-axis is shaded and labelled with a plus sign.