Help with Maths please - changing a formula?

2012-09-09 6:57 pm

I am trying to do my Maths homework but am stuck on this one question.
I need to change the formula for volume of a cone V=⅓πr²h so that there are no r's in it.
I know that the radius of this cone is 12 and the hight is 18.
I think it might have something to do with using tan, but I'm not sure.

Thank you!

更新1:

I need to change the fomula so that the r's are replaced by h's.

更新2:

I need to change the fomula so that the r's are replaced by h's.

回答 (4)

[匿名]

2012-09-09 7:06 pm

✔ 最佳答案

tanθ = r/h = 12/18 = 2/3
r = 2h/3
V = 1/3 πr²h = 1/3 π(2h/3)²h
= 1/3 π(4/9)h³
= 4/27 πh³

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[匿名]

2012-09-09 7:11 pm

If height is h and radius r, we get the angle as tan-1(r/h)

Or, tan-1(2/3) = r/h or h = r/{tan-1(2/3)}.

Hence V = (1/3)*pi*r^3/tan-1(2/3).

Piyush is also correct, in that case you have to replace h with (3/2)*r. Piyush solved it for h.

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[匿名]

2016-10-18 9:35 pm

multiply both elements by 3: 3p= 2(m-4) then multipy out the brakcets 3p=2m-8 upload 8 to both ingredient 3p+8=2m divide both elements by 2 (3p+8)/2=m then m is the priority wish i helped

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Como

2012-09-09 7:04 pm

Sorry but this question makes no sense.
Change the formula to what?

Out of interest
V = (1/3) π x 12² x 18
V = 2714.3 units³

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