How Do You Apply the Midpoint Rule for Riemann Integration?

[blank09]

I am having troubles doing the midpoint rule.. i guess I just need a step by step explanation. for instance

n=3 a=1 b=3 x^2 dx

approximate

 

[ZioX]

Riemann integration for x^2 on the interval (1,3)? Divide your interval into 3 equal sections, determine the middle of each section. Sum the area of the rectangles generated by the height determined by the value of x^2 at the midpoint and the appropriate base.

Really now, this is probably in your textbook.