Area under Curve as sum of subdivided rectangles to limits

Lew W.S.
This applet shows that area under a curve can be found subdividing into rectangles. By increasing subdivisions, the lower and upper estimate of the areas of the rectangles converge to (reaches) the same value as the exact value by integration calculus method.
Use the input box to enter the function and upper and lower limits (left and right limits of the shaded area) Use the slider numdiv or the input box captioned Number of Divisions to enter how many rectangles (subdivisions) you wish to use to estimate the area under the curve.