This does trapezoid approximations of integrals.  To use, input the equation at the Y1= prompt, beginning with ", for example it will look like    Y1= "2x   Then, put in the endpoints and the number of trapezoids.  It outputs the sum, and leaves the following in the lists.  L1: X values at the edge of each trapezoid L2:value of F(X)
L3: value doubled.