The function is , .

Number of subintervals are .

Width of the interval is and .

Sample points to be left end points.

Left end points are and .

Riemann sum is \ \

Graph:

Graph the function and left endpoints.

Here Riemann sum represents the area under the curve. \ \

Area under the curve is area of the rectangle using left endpoints.

The Riemann sum represents the sum of the areas of the two rectangles above the axis minus the sum of the areas of the three rectangles below the axis.

Riemann sum is net area of the rectangles with respect to axis.

Riemann sum is .