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#2 2005-11-28 00:20:14
- mathsyperson
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Re: Re-arranging!!!
All of the /3's in the second term can be combined into a /27.
V = 1/3πr²h - 1/27πr²h
These two terms are now identical apart from the constant at the front, so they can be combined:
V = 8/27πr²h
To get r² on its own, divide the right-hand side by everything except it:
27V/(8πh) = r²
To get r, just square root both sides:
√[27V/(8πh)] = r
Why did the vector cross the road?
It wanted to be normal.
#5 2005-11-28 07:34:51
- MathsIsFun
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Re: Re-arranging!!!
Surface Area?
Does this relate to your question I got part way through here: http://www.mathsisfun.com/forum/viewtopic.php?id=2002 ?
I am sorry, I just haven't had time to finish it.
"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman
#6 2005-11-28 07:47:58
- mathsyperson
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Re: Re-arranging!!!
That can't be a measure of surface area.
Every term in a surface area formula has to include exactly 2 lengths.
πr only has 1 length and (r² + 2025/πr²)² is either a contradiction in itself, or it contains 4 lengths, which would be impossible anyway. Are you sure the formula is right?
Why did the vector cross the road?
It wanted to be normal.
#7 2005-11-28 20:02:26
- johny
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Re: Re-arranging!!!
Mathsyperson: Your right this isnt the formula for the Surface area.........but according to my question i had to substitute the height H of Volume to the surface area.
as the formula is S.A= Pi*R*S ...........and s= square of [R2+H2]......so i substituted the height in this formula. Which came to the above term. can it be simplified more???
Last edited by johny (2005-11-28 20:02:57)
#8 2005-11-28 20:23:31
- mathsyperson
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Re: Re-arranging!!!
In my previous post, I must have imagined that you had a plus sign in there, which you didn't. There's actually only one term, but it has 5 lengths, which is still wrong.
If you square rooted the bit inside the square brackets then you would get 2 lengths, which is perfect.
S.A. = π*r*√[r² + (2025/π)r²]
That can be simplified more by combining the two terms inside the bracket to give [(2025/π+1)r²]
The r² can then be taken out of the square root:
S.A. = π*r²√(2025/π+1)
Why did the vector cross the road?
It wanted to be normal.