Detailed description

A part of the graph of y = x squared is shown. There I s a vertical dotted line at x = 1. The points ((i-1)/n, 0) and (i/n, 0) are shown. Two rectangles are drawn with two vertices at ((i-1)/n, 0) and (i/n, 0). The smaller rectangle has height  (i-1) squared over n squared and the larger has height i squared over n squared. Both rectangles have one vertex on y = x squared.