The area under a curve is approximated by dividing it into trapeziums of equal width.
The trapezoidal rule gives the sum of the areas of these trapeziums. Check out KeysToMaths1 for more tutorials and worked solutions: https://www.youtube.com/channel/UCOYoe9L9R13HGUIhszjkeug
Worked sample problem, finding the volume of a solid prism. More free lessons at: http://www.khanacademy.org/video?v=eF6zYNzlZKQ Note: All Khan Academy content is available for free at (www.khanacademy.org)