Swern's Rectangle Estimate Comparison

Move the slider around to change the number of rectangles used in estimating the area under the curve.
1. How is the Leftsum estimate affected when you slide points A and B around? 2. How does the Leftsum estimate compare to the actual value of the integral as you adjust the number of rectangles? 3. How many rectangles would we need to have the estimate be exactly the same as the actual integral value?