Geometry help- Cavalier's Principle?

Question

What is Cavalier's Principle?

Answer 1

The correct spellings are Cavalieri's Principle.
Bonaventura Francesco Cavalieri (in Latin, Cavalerius) (1598–November 30, 1647) was an Italian mathematician known for Cavalieri's principle, which states that the volumes of two objects are equal if the areas of their corresponding cross-sections are in all cases equal. Two cross-sections correspond if they are intersections of the body with planes equidistant from a chosen base plane. The principle was originally discovered by Zu Chongzhi about 1,000 years ago [citation needed]. Cavalieri's developed a "method of the indivisibles", which he used to determine areas and volumes. It was a significant step on the way to modern infinitesimal calculus.
Theres a nice example with an illustration here:
http://www.jimloy.com/cindy/cavalier.htm
Thanks.`