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Samsonite

Some help with calculating the volume of a cone?

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Hello, and thanks for reading this! I need to know if what I do is right. I want to calculate the volume of a cone. And I know that the formulae for calculating a figure like that is;
V = PIr^2h/3



and I try to do like this:
PIr^2h/3 = V
r^2/PI h  = V * 3/PI h
r^2         = V * 3/PI h
sqrt(r^2) = sqrt(V*3/PIh)
r             =sqrt(V*3/PIh)



Err...thats how I do it. And I would like to know if it's the right answer, or what I do wrong. Wich operations do I do first etc, would be nice to hear. I'm kinda lost. Cheers, and thanks for reading through! [smile]

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A torus could be seen here (and the formula for its volume also):
http://mathworld.wolfram.com/Torus.html

But it has nothing to do with triangles. And the volume formula doesnn't match. So perhaps the thing you have is something different. Could you post a sketch?

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Quote:
Original post by Samsonite
Aha! Got it, cones, thats the right word!

Then, of course, look here:
http://mathworld.wolfram.com/Cone.html

;-)

V = 1/3 Pi r^2 h
is correct.

But then
r = sqrt( V * 3 / ( Pi h ) )
so that your formula lacks a pair of braces.

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Thank you!

But is my little work above correctly set up? Does it miss something. I'm trying to find the length of radius r.

Thanks for helping me this far [smile]

EDIT: Thats wonderful! I love this board, thanks so much for the help!

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Sorry, but your way of computation isn't totally correct. From the volume
V = 1/3 Pi r^2 h
3 V = Pi r^2 h
3 V / Pi = r^2 h
3 V / Pi / h = 3 V / ( Pi h ) = r^2
r = +/- sqrt( 3 V / ( Pi h ) )
where the negative solutiom is nonsense here, so that
r = sqrt( 3 V / ( Pi h ) )
remains.

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Allright, I seem to get the answer right. But there are some parts of your computation that I don't do, f. ex.


3 V / Pi = r^2 h
3 V / Pi / h = 3 V / ( Pi h ) = r^2



I merge these two. Creating:


3 V / (Pi h) = r^2



Right away.

Is your way the ones they use at colleges or universities? My teacher tells me that my answer is right but my computation really sucks...I just need to hear it from someone else. Perhaps from the games industry. [smile]

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There is no problem in doing several steps at once, of course. I've written it each single step just to make it clear. (However, I'm an Electrical Engineer and not of the game industry, sorry ;-)

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