A Riemann sum is an approximation of the form . It is most often used to approximate the area under some function on the closed interval . Below are six types of sums: left-hand, midpoint, right-hand, trapezoidal, lower, and upper.

In these sums, represents the width of each rectangle (AKA interval), defined by . The parameter that changes depending on the type of sum is . This determines where the function is evaluated and thus calculates the height of each rectangle.

• Left-hand:
• Midpoint:
• Right-hand:

A trapezoidal sum differs from the previous 3 in that is the average of the endpoints of each interval evaulated in

• Trapezoidal: where

As , these approximations tend to the actual area between the function and x-axis which is given by: