Long description
The figure shows Cartesian axes labelled x and y and is concentrated in the upper-right quadrant. The graph of y equals x squared is drawn and labelled. Points a and b are labelled on the positive x-axis with a being nearer the origin. The line joining these two points on the x-axis is a bold line. The two points have vertical lines drawn to meet the parabola y equals x squared. The area under the graph and above the positive x-axis is shaded.