In this sheet, users can adjust the upper and lower boundaries by dragging the red points along the x-axis. They can also enter in their own two functions to see how the area between the two curves is calculated. The applet does not break the interval into two separate integrals if the upper and lower functions switch roles. User should note that the when the area of the shaded region begins to decrease, this is the x-value where the integral should be broken up.