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Some concepts regarding area that I need help understandingby fwb
Tags: concepts 
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#1
Sep2606, 09:59 PM

P: 3

Most 3d volume formulas look similar to their corresponding 2d area formulas for a particular shape. How does calculus, specifically integration, relate the two sets of formulas?
For example: how is the formula of a cone derived from the formula of a circle? 


#2
Sep2706, 02:45 PM

Sci Advisor
P: 6,027

One method: 3d coordinate system  put cone point at origin and cone axis along positive x axis. Let h be height of cone and R=radius of base. Let k=R/h. The radius of the cone circle defined by a plane at point x perpendicular to the x axis is given by r=kx. The differential of volume at a point x is then pi*r^{2}dx. Integrate from 0 to h and the volume will be pi*k^{2}h^{3}/3=pi*R^{2}h/3.
There may be neater ways, but you can see the point. 


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